Update Ruby and Freeglut versions.
Fix typos.
Use function parameter declaration according to ANSI C.
Replace deprecated rb_thread_blocking_region() by rb_thread_call_with_gvl()
Link to both freeglut libraries and opengl, so that there are no unmet dependencies at build time for the windows build.
Add x64-mingw cross build.

Use mini_portile for building freeglut to simplify build tasks.
Enforce static linking of freeglut in windows binary gem.
Don't pollute the global namespace.
Update History.rdoc
Bump VERSION to 8.2.0
Strip dll files for binary windows gems.