Revert "Replace RMagick by ChunkyPNG"

This reverts the following commits:

* 291ce4bb5f7a8afd57ad7d82094865f3c8bbc4a4
* 4a423112885a516dbdd26b0bd3fa074fac6124c8
* 27c2c41fd48085b917f65278c3fa5d8156c79bc7
* ea3c056094432499af024cccc3cc81801d40ed36
* 2a0d0aea12d6b147f09fabd7abed4389fe3aeb7c
Add basic support for including SVG images inside the sprite.
Update example CSS.
Fix README commands.
Add `.svg` scoped styles placeholders.
Embedded SVG images directly inside the stylesheets.
Merge branch 'master' into svg-support

Conflicts:
	lib/spriteful/sprite.rb
	spec/stylesheet_spec.rb
Add support for SVG optimization.
Bring the Gemfile.lock to the repo.
Remove unused variable from bad merge.
Update SVG example css.
:scissors:
Add `svg_optimizer` to the gemspec.
Merge branch 'master' into svg-support
Add some notes about SVG support on the README.
Scumbag `--deployment` flag.
Merge branch 'master' into svg-support

Conflicts:
	spec/stylesheet_spec.rb
Merge pull request #7 from lucasmazza/svg-support

Convert SVG to PNG