Texture binding + creation

Closes #49
Are you sure about this parameter? If that's the same way in hgl-rs, has anyone worked with textures there?
AFAIK, this is the level you want to set up the data for, *not* the total number of mipmap levels. Typically, we'd want to setup level 0 and then generate mipmap chain. In anyway, passing the maximum number there barely makes any sense.