The filter_audio API is not working for qTox/Tox and thus disabled by default via compiler switch. In current qTox UI, it is not configurable, even when this switch is enabled. According to issue #3194 the library is no longer maintained as well. I don't see any reason to keep it in qTox.
Fixed install_libfilteraudio.sh to work on windows
bootstrap.bat now invokes sh bootstrap.sh (for convenience)
Updated INSTALL.md to reflect simplified bootstrapping procedure