Fix transparent svg png fallbacks
Use .svgasimg for feature detection

* It's a sync test in modernizer head
* Seems to be a better heuristic for svg support 
in background-image than svg that simply tests
for basic svg support. ( Technically there is no
way to detect for svg support in background-image
but it seems that browsers have implemented this at
the same time as svg in img)
Add an option to skip svg optimization
Update documentation
Base64 encode the data-uri for IE9 Support
Readme changes
Pass optimise flag into Image as an option
Revert "Use .svgasimg for feature detection"

This reverts commit 4bd5845d2dd5eccc1d7b33dfc140b7c8cdec2a4c.
Revert README changes
Add doc for optimize option.
Merge pull request #14 from reevoo/master

A few fixes for SVG features . . .