Svg

inline-image has only supported binary encoded images, this adds initial support for SVG.  SVG's are commonly base64 encoded around the internet, even at the cost of additional file size (10-30%): http://calendar.perfplanet.com/2014/tips-for-optimising-svg-delivery-for-the-web/.  This adds support for base64 encoded svg and url escaped svg.

    inline-image('file', $encode: false);

TODO:
- [ ] Documentation updates
- [ ] Testing and more testing does url.Parse properly encode svgs?
- [ ] Refactor spritewell for taking care of more work in svg inlining
- [ ] Should svg's be spriteable?