This library wraps the ffmpeg library and adds some utility
functions and types.

mingw-w64 has its own pthreads library

Originally I made the "win_pipe" stuff for named pipes on windows but it
was argued that it should be available to all modules and
programs/libraries that the modules might communicate with.

It cannot really be put in to libobs due to the fact that there would
hypothetically be things unrelated to libobs that might want to use it,
so I felt the best option was just to create a simple static library
specific for interprocess communication.

Non-windows versions of these functions are still yet to be implemented.

CMake now works on all platforms