Ensure everything is tested on travis

`cargo test` does not test dependencies
Fix warnings
Remove SubMesh type

This currently is not used for anything
Merge pull request #281 from bjz/submesh

Remove SubMesh type
Merge pull request #280 from bjz/tests

Ensure everything is tested on travis
Added frame example

A short example showing how to setup and render to a frame based on the cube example
updated frame example to match cube example
merged cube and frame example