using glad for opengl
removed simple test of glad
added missing include/ files from glad
No more immediate mode! VBOs! New Texture!

Texture no longer depends on SDL's Texture capabilities, and supports 24-
and 32-bit color.

TileLayers now use OpenGL Vertex Buffer Objects (VBOs) to upload its data
less frequently and more efficiently. (Right now, use the new
refreshTiles() method to do the upload.)
removed crappy sequential tile test
reenabled alpha blending
Merge pull request #1 from hdon/master

Still needs some work but it works fine on my system, merging hdon's work