Allow relatively fast partial updates to a terrain by modifying the heightmap image and calling ApplyHeightMap(). Added WorldToHeightMap() function to Terrain for converting world coordinates to heightmap pixel positions.
Remove unused variable. Fix Terrain Lua binding.
Travis CI: API documentation update at 2014-06-20 23:21:27 UTC.
[ci package]
For Travis CI - switch CI build to use OS X build environment.