improve exception documentation
improve state_view default handlers
add SAFE_PROPAGATION defines for compiling C++ as Lua
add examples for automatic operator registrations and as_container
fix tutorial code
change tests to not throw unless absolutely necessary
provide synchronization for file writing in tests
provide thread safety around thread tests for REQUIRE
add ostream automatic support
change 5.1 compat to only kick in luaL_loadbufferx and luaL_loadfilex when LuaJIT is version 2.0.1 and lower
added variadic_results, to return a variable number of arguments to Lua
added variadic_results and as_results
added improved function examples (for multiple results and split overloading out)
added tests for variadics
added tests for C++17 utilities
added a forwarding header
added a specific `unsafe_function` header
added and improved documetation pages