Remove invalid SASS expression from specs

The original sass-spec contains a test case which uses invalid
pseudo-selector, which is being ignored by the original SASS
implementation.

That case is being removed in this commit, since it
doesn't bring value to the end user and only introduces deliberate bugs
into the codebase.
Remove unneeded Data.Char imports
Add basic specs for hexColorShort parser
Add TODO about removing duplicates from the tests