Texture binding + creation

Closes #49
Each mip level is not an axis. All mip levels form the third axis. That's why it's called trilinear, AFAIK.

Regards,
Dzmitry

> On Jul 19, 2014, at 14:19, Corey Richardson <notifications@github.com> wrote:
> 
> In src/device/tex.rs:
> 
> > +//! "Texture" is an overloaded term. In gfx-rs, a texture consists of two
> > +//! separate pieces of information: image storage description (which is
> > +//! immutable for a single texture object), and image data. To actually use a
> > +//! texture, a "sampler" is needed, which provides a way of accessing the
> > +//! texture data.
> > +
> > +use std::default::Default;
> > +
> > +/// How to [filter](https://en.wikipedia.org/wiki/Texture_filtering) the
> > +/// texture when sampling. They correspond to increasing levels of quality,
> > +/// but also cost. They "layer" on top of each other: it is not possible to
> > +/// have bilinear filtering without mipmapping, for example.
> > +///
> > +/// These names are somewhat poor, in that "bilinear" is really just doing
> > +/// linear filtering on each axis, and it is only bilinear in the case of 2D
> > +/// textures. Similarly for trilinear, it is really Quadralinear(?) for 3D
> Well, it samples on each of the axis, and then across two mipmap levels, if I am not mistaken. Thus, 4 dimensions of sampling.
> 
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