Capture regular expression groups when lexing.

As certain token constructs represent elements being wrapped—such as text being wrapped in enclosing quotes—the parser step would need to pre-process the token to remove the quotes and identify flags (in the case for Python-style prefixed strings anyway.  Why do the work twice?

The attached changes add slots and update `__repr__` implementations where needed, and include a test for the "quoted string" case, demonstrating use.  Documentation is also updated to clearly demonstrate the "quoted string" use case and update the presented object `repr` output.