add char name lookup aliases (LF,FF,CR and NEL)

The Perl 6 spec and therefore roast says that e.g. \c[LF] is identical to
\c[LINE FEED (LF)]. MoarVM already got a similar patch:
https://github.com/MoarVM/MoarVM/commit/339d547cdd0bec45e2ac3f6d97fb6b9b77bdfce0
And it would be nice if Parrot would get this ability, otherwise we would
have to do it in a rather slowish way in nqp.