backfill key table with GLFW constants

With the OS X key table as a basis, entries were populated with GLFW constants. A quick smoke test was performed by zipping through the keys on a Apple Wireless Keyboard with a Cinder app within VMWare, but something more substantial might be warranted, especially the keypad.
Merge pull request #1 from pizthewiz/glfw-keytable

GLFW key table for Linux