These stubs are largely implemented the same: their API is exposed, but
they print to the debug console and sometimes `TODO()`. These changes
allow GLU and Tux Racer to build.
Methods stubbed:
* `glTexImage1D`
* `glTexImage3D`
* `glTexCoord2d(v)`
* `glNormalPointer`
* `glTexGen(d|f|i)`
* `glTexGenfv`
This controls how fetched texels are combined with the color that was
produced by a preceding texture unit or with the vertex color if it is
the first texture unit.
Currently only a small subset of possible combine modes is implemented
as required by glquake.
Textures are now initialized with a nullptr upon generation.
They are only actually created once they are bound to a target.
Currently only the GL_TEXTURE_2D target is supported.
The software rasterizer now allows rendering with or without
a bound TEXTURE_2D.
