Added gd and Imagick support.
Implemented image adapters for GD and ImageMagick (ref #10).
Fix styles
Fix namespacing errors
Add basic adapter class & rename classes.
Add getResource method
Change exception messages
Allow multiple calls of destroy().
Fix Imagick image loading
Fix invalid alpha values with Imagick.
Add tests for adapters
Fix style
Refactor ImageLoader
Install Imagick extension on travis
Fix travis setup
Don't install imagick on HHVM
Update composer.json
Merge branch 'pr/10'