Added in the failed POSIX permit object proposal from source.
Got it compiling with modern libraries and compilers.
Replaced all use of Intel TBB with OpenMP.

Fixed up some sloppiness in use of read()/write() to interact with system fds.

Now compiles without warnings on both GCC and clang.
Fixed up more sloppiness on Windows.
Added unit test to ensure that destroying permits being waited upon in other threads works as intended.