Added install instructions for cross-compiling to Windows

INSTALL.md

@@ -6,6 +6,11 @@
       - [Homebrew](#homebrew)
       - [Non-Homebrew](#non-homebrew)
     - [Windows](#windows)
+      - [Cross-Compile](#windows-cross-compile)
+        - [Setting up a VM](#windows-cross-compile-vm)
+        - [Setting up the environment](#windows-cross-compile-environment)
+        - [Compiling](#windows-cross-compile-compiling)
+      - [Native](#windows-native)
 
 - [Additional](#additional)
     - [Advanced configure options] (#aconf)
@@ -176,12 +181,182 @@ http://caiustheory.com/install-gcc-421-apple-build-56663-with-xcode-42
 <a name="windows" />
 ###Windows:
 
+<a name="windows-cross-compile" />
+
+####Cross-compile
+
+It's a bit challenging to build Tox and all of its dependencies nativly on Windows, so we will show an easier, less error and headache prone method of building it -- cross-compiling.
+
+<a name="windows-cross-compile-vm" />
+#####Setting up a VM
+
+We will assume that you don't have any VM running Linux around and will guide you from the ground up.
+
+First, you would need to get a virtual machine and a Linux distribution image file.
+
+For a virtual machine we will use VirtualBox. You can get it [here](https://www.virtualbox.org/wiki/Downloads).
+
+For a Linux distribution we will use Lubuntu 14.04 32-bit, which you can get [here](https://help.ubuntu.com/community/Lubuntu/GetLubuntu).
+
+After you have those downloaded, install the VirtualBox and create a VM in it. The default of 512mb of RAM and 8gb of dynamically-allocated virtual hard drive would be enough.
+
+When you have created the VM, go into its **Settings** -> **System** -> **Processor** and add some cores, if you have any additional available, for faster builds.
+
+Then, go to **Settings** -> **Storage**, click on **Empty** under **Controller: IDE**, click on the little disc icon on the right side of the window, click on **Choose a virtual CD/DVD disk file** and select the downloaded Lubuntu image file.
+
+Start the VM and follow the installation instructions.
+
+After Lubuntu is installed and you have booted into it, in VirtualBox menu on top of the window select **Devices** -> **Insert Guest Additions CD image...**.
+
+Open terminal from **Lubuntu's menu** -> **Accessories**.
+
+Execute:
+```bash
+sudo apt-get update
+sudo apt-get install build-essential -y
+cd /media/*/*/
+sudo ./VBoxLinuxAdditions.run
+```
+
+After that, create a folder called `toxbuild` somewhere on your Windows system. The go to **Devices** -> **Shared Folders Settings...** in the VirtualBox menu, add the `toxbuild` folder there and set **Auto-mount** and **Make Permanent** options.
+
+Execute:
+```bash
+sudo adduser `whoami` vboxsf
+```
+Note the use of a [grave accent](http://en.wikipedia.org/wiki/Grave_accent) instead of an apostrophe.
+
+Then just reboot the system with:
+```bash
+sudo reboot
+```
+
+After the system is booted, go to **Devices** -> **Shared Clipboard** and select **Bidirectional**. Now you will be able to copy-paste text between the host and the guest systems.
+
+Now that the virtual machine is all set up, let's move to getting build dependencies and setting up environment variables.
+
+<a name="windows-cross-compile-environment" />
+#####Setting up the environment
+
+First we will install all tools that we would need for building:
+```bash
+sudo apt-get install build-essential libtool autotools-dev automake checkinstall check git yasm pkg-config mingw-w64 -y
+```
+
+Then we will define a few variables, **depending on which you will build either 32-bit or 64-bit Tox**.
+
+For 32-bit Tox build, do:
+```bash
+WINDOWS_TOOLCHAIN=i686-w64-mingw32
+LIB_VPX_TARGET=x86-win32-gcc
+```
+
+For 64-bit Tox build, do:
+```bash
+WINDOWS_TOOLCHAIN=x86_64-w64-mingw32
+LIB_VPX_TARGET=x86_64-win64-gcc
+```
+
+This is the only difference between 32-bit and 64-bit build procedures.
+
+For speeding up the build process do:
+```
+MAKEFLAGS=j$(nproc)
+export MAKEFLAGS
+```
+
+And let's make a folder where we will be building everything at
+```bash
+cd ~
+mkdir prefix
+cd prefix
+PREFIX_DIR=$(pwd)
+cd ..
+mkdir build
+cd build
+```
+
+<a name="windows-cross-compile-compiling" />
+#####Compiling
+
+Now we will build libraries needed for audio/video: VPX and Opus.
+
+VPX:
+```bash
+git clone http://git.chromium.org/webm/libvpx.git
+cd libvpx
+git checkout tags/v1.3.0
+CROSS="$WINDOWS_TOOLCHAIN"- ./configure --target="$LIB_VPX_TARGET" --prefix="$PREFIX_DIR" --disable-examples --disable-unit-tests --disable-shared --enable-static
+make
+make install
+cd ..
+```
+
+Opus:
+```bash
+wget http://downloads.xiph.org/releases/opus/opus-1.1.tar.gz
+tar -xf opus-1.1.tar.gz
+cd opus-1.1
+./configure --host="$WINDOWS_TOOLCHAIN" --prefix="$PREFIX_DIR" --disable-extra-programs --disable-doc --disable-shared --enable-static
+make
+make install
+cd ..
+```
+
+Now we will build sodium crypto library:
+```bash
+git clone https://github.com/jedisct1/libsodium/
+cd libsodium
+git checkout tags/0.4.5
+./autogen.sh
+./configure --host="$WINDOWS_TOOLCHAIN" --prefix="$PREFIX_DIR" --disable-shared --enable-static
+make
+make install
+cd ..
+```
+
+And finally we will build Tox:
+```bash
+git clone https://github.com/irungentoo/toxcore
+cd toxcore
+./autogen.sh
+./configure --host="$WINDOWS_TOOLCHAIN" --prefix="$PREFIX_DIR" --disable-ntox --disable-tests --disable-testing --with-dependency-search="$PREFIX_DIR" --disable-shared --enable-static
+make
+make install
+cd ..
+```
+
+Then we make Tox shared library:
+```bash
+cd "$PREFIX_DIR"
+mkdir tmp
+cd tmp
+$WINDOWS_TOOLCHAIN-ar x ../lib/libtoxcore.a
+$WINDOWS_TOOLCHAIN-ar x ../lib/libtoxav.a
+$WINDOWS_TOOLCHAIN-ar x ../lib/libtoxdns.a
+$WINDOWS_TOOLCHAIN-gcc -Wl,--export-all-symbols -Wl,--out-implib=libtox.dll.a -shared -o libtox.dll *.o ../lib/*.a /usr/$WINDOWS_TOOLCHAIN/lib/libwinpthread.a -lws2_32 -static-libgcc
+```
+
+And we will copy it over to the `toxbuild` directory:
+```bash
+mkdir -p /media/sf_toxbuild/release/lib
+mv libtox.dll* /media/sf_toxbuild/release/lib
+mkdir -p /media/sf_toxbuild/release/include
+mv ../include/tox /media/sf_toxbuild/release/include
+```
+
+That's it. Now you should have `release/lib/libtox.dll` and `release/include/tox/<headers>` in your `toxbuild` directory on the Windows system.
+
+<a name="windows-native" />
+####Native
+
+Note that the Native instructions are incomplete, in a sense that they miss instructions needed for adding audio/video support to Tox. You also might stumble upon some unknown MinGW+msys issues while trying to build it.
+
 You should install:
   - [MinGW](http://sourceforge.net/projects/mingw/)
 
 When installing MinGW, make sure to select the MSYS option in the installer.
-MinGW will install an "MinGW shell" (you should get a shortcut for it), make
+MinGW will install an "MinGW shell" (you should get a shortcut for it), make sure to perform all operations (i.e., generating/running configure script, compiling, etc.) from the MinGW shell.
-sure to perform all operations (i.e., generating/running configure script, compiling, etc.) from the MinGW shell.
 
 First download the source tarball from https://download.libsodium.org/libsodium/releases/ and build it.
 Assuming that you got the libsodium-0.5.0.tar.gz release:
@@ -194,8 +369,7 @@ make install
 cd ..
 ```
 
-You can also use a precompiled win32 binary of libsodium, however you will have
+You can also use a precompiled win32 binary of libsodium, however you will have to place the files in places where they can be found, i.e., dll's go to /bin headers to /include and libraries to /lib directories in your MinGW shell.
-to place the files in places where they can be found, i.e., dll's go to /bin headers to /include and libraries to /lib directories in your MinGW shell.
 
 Next, install ProjectTox-Core library, should either clone this repo by using git, or just download a [zip of current Master branch](https://github.com/irungentoo/ProjectTox-Core/archive/master.zip) and extract it somewhere.
 
@@ -335,4 +509,3 @@ Install on ubuntu:
 ```bash
 sudo apt-get install ncurses-dev
 ```
-