Move wrap_gl* prototypes into top-level include/gl_wrap.h

Move the wrap_gl* prototypes into the top-level file include/gl_wrap.h, which also #defines the functions to the gl* equivalents on non-Windows.
This allows replay_draw.hpp to be Windows-only again, and moves platform-independent code out of the Windows files.
Pass a 'void *' to the wrap_gl* functions rather than wincount_t

Instead of passing wincount_t to the wrap_gl* functions, pass a 'const void *' pointer in case other platforms need to pass something more complicated.
This also allows the GLUT target to build without using any of the Windows-specific files.