Partial port to opengl.

I forgot how much opengl sucked, so I figured I might try a port.

Nvidia doesn't draw (must be some fragment binding issue?, randomlulz returns GL_INVALID on glAttribPtr as well)
Intel doesn't compile the shader (and the error message makes no real sense. wut?)
Amd driver simply crashes (wheehaa)

All and all, doesn't look like much has changed in opengl the past 10 years, apart from even uglier initialization and more fragmented specs ~
Call correct Texture/texture2d
Fix rendering: GL3+ needs VAO, initialize screen_width/screen_height

*yay* it works now *dances*
Update gitignore
Isolate GLES, add DESKTOPGL option to core.mk
Merge branch 'skmp/gl3.1'