Unstoppable Okapi

Add:

• Add support for JSON encoding and decoding using lua-cjson.

Change:

• Add support for additional OpenGL versions including OpenGL ES.
• Add support for running in a web browser with WebVR.

Fix:

• Fix potential crash when loading equirectangular skyboxes.
• Fix crash on windows if the save directory does not exist.

Remove:

• Remove headset bounds visibility functions.