Since C++11 threads are available on every platform that has threads, we
no longer need our pthread implementation. The LOL_FEATURE_CXX11_THREADS
macro is gone, too, and we now just use LOL_FEATURE_THREADS.

Note that it is still necessary to link with -lpthread or -pthread on
some platforms, so we don’t throw that part away.

Add mingw-std-threads project to external/ for full C++11 thread support, fix
an incorrect Win32 fix I did in PEGTL, work around mingw’s <io.h> declaring a
conflicting eof symbol, and fix a capitalisation error in log.cpp.

My Ludum Dare 32 entry is now in the main games/ directory and is
called “Size-o-Tron 3000” because… because, that’s all.

This will be a 2D puzzle platformer. The theme this year is
“Unconventional Weapon”.

MeshViewer first pass

Lock/Unlock mechanism safer, and implement the rule of three.