Merge pull request #22 from bvssvni/master

Added `vao` to constructor
Merge pull request #23 from bvssvni/master

Return Err if can not open path in `Texture::from_path`
Add a way to clear a shader
Merge pull request #25 from oliviertremblay/master

Add a way to clear a shader (Resolves #24)
Upgraded to latest Rust-Empty