Add rx symbol for regexp literals
Treat regexp literals as strings in proper contexts

Mark regexp literals as strings by modifying the syntax table
properties, to make them play more nicely with sexp navigation.
Notably, forward-sexp will not move across the entire regexp literal.

Also limit the fontification and treatment of regexp literals to
contexts in which they are allowed, that is, in cases or selectors, node
names, and after match operators.
Restore our special face for regexp literals
Put property on body of regexp literal

Font lock keywords would miss the property change otherwise
Use generic string class

Recommended by the Emacs Lisp reference
Add unit tests for our new regexp handling
Merge pull request #39 from lunaryorn/rework-regexp-highlighting

Redesign regular expression handling