whoops
Fixes bug where --ignore-sass-mixins isn't respected in @imports

There is a `@children.empty?` edgecase that I can't recreate in the
tests but I'm seeing on a private codebase. It would be nice to
red/green test that bit of the conditional.

refs: #62
Bumping version to 1.3.1
Fixes attribute parsing bug where comments include braces

Also refactored out the dynamic bit in favor of present?/absent? logic.
Slowly getting the hang of those conditionals.

refs: #29
Adds ruby-version

This is rvm and rbenv agnostic
Added blurb on why csscss doesn't remove duplications
Merge branch 'master' into gh-pages
Adds blurb to jekyll