Bugfix release - improve C/C++ interop and build integration

Fixed
Added extern "C" guards to all exported functions so PAL can now be linked from both C and C++ projects.
Fixed a condition variable bug where the wrong thread could acquire the mutex first, causing intermittent locking issues. See tests/condvar_test.c
Updated premake scripts to allow PAL to be included as a submodule or directly in another workspace if the build system is premake.

Notes
No API or ABI changes
Safe upgrade from v1.0 - just rebuild your project after updating.