Merge pull request #174 from bvssvni/master

Upgraded to latest Rust
Fixed issue with as_slice
Merge pull request #175 from gchp/slice-issue

Fixed issue with as_slice
Renamed RelativeTransform2d to RelativeTransform

Closes #178
Merge pull request #179 from leonkunert/master

Renamed RelativeTransform2d to RelativeTransform
Use `glyph_cache` from opengl_graphics