Text rendering

Are there plans to include this functionality?

It could be done using `wgpu_glyph`, but this [requires the `wgpu::Device` handle to be exposed](https://github.com/hecrj/wgpu_glyph/blob/master/src/builder.rs#L111) (a simple method on `rgx::core::Device` would suffice I think).

Start by reading the wgpu_glyph builder.rs reference around line 111 and inspect rgx::core::Device to understand the requested handle exposure. Determine whether text rendering is planned and how the library should integrate it; done means an agreed implementation scope, not merely exposing the handle.

Written by the indexing model from the issue text.