Order CSS rules by pseudoclass importance
tag (released) 1.5.1 version and prepare 1.5.2 branch for upcoming changes
added support for .ico files when using rmagick [issue #18](https://github.com/jakesgordon/sprite-factory/pull/18)
Merge branch 'pseudo_classes' of https://github.com/amberbit/sprite-factory into sorting
added tests to ensure css rules are ordered by (a) classname and (b) psuedoclass importance (for #20)
Simplified pseudoclass importance sort ordering (for #20)
added test to ensure :focus pseudoclass image goes in correct order of importance relative to other pseudoclasses
Provide a new customization option to solve issue #21 - when generating SASS files use image-url instead of url

Replaced legacy :csspath option with a new :cssurl option that allows customization of the full background url
attribute, **including** the "url()" part (e.g. not just the path)

Example, specify:

    :cssurl => "image-url('$IMAGE')"

or

    :cssurl => lambda {|image| "image-url('#{image}')" }

to generate styles that looks like:

    background: image-url('output.png') ...

instead of the default:

    background: url('output.png') ...

(see updated README for more details about using the new option)
updated README and RELEASE_NOTES for new `:cssurl` option
Update README.md
noted release date for 1.5.2