Add spec for new colors (rebeccapurple and transparent)

https://github.com/sass/libsass/issues/699
https://github.com/sass/libsass/issues/700
Add specs for issue 702
Merge pull request #160 from mgreter/spec/issues/700

Add spec for new colors (rebeccapurple and transparent)
Merge pull request #161 from xzyfer/feat/issue-702

Add specs for issue 702
Added charset directive to string specs to prevent some edge issues
Added spec for LibSass issue 733