Reimplement ChordRepetition facility.

Reimplement ChordRepetition facility.

Remove basically all configurability.  Reduce parser and lexer support
to hardwired minimum.  Don't track the last chord in the lexer/parser.
Instead establish it at toplevel-music-functions level if the user has
not already called \chordRepeats to do so himself.

Addresses issue 1110 and my sense of aesthetics.