Merge pull request #2 from bvssvni/master

Moved in `gfx_graphics::Texture`
Merge pull request #4 from bvssvni/master

Added .travis.yml
Added build status button

Closes https://github.com/PistonDevelopers/gfx_texture/issues/3
Added `Texture::from_rgba8`

Closes https://github.com/PistonDevelopers/gfx_texture/issues/5