Merge pull request #3 from bvssvni/master

Moved in `graphics::ImageSize`
Merge pull request #5 from bvssvni/master

Added .travis.yml
Added Travis CI build status
Merge pull request #7 from bvssvni/master

Added `FromMemoryAlpha` trait
Added `get_width` and `get_height` to `ImageSize`

Closes https://github.com/PistonDevelopers/texture/issues/8

* Fixed doc comment
* Fixed compiler warning about missing docs