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.

[dak, 2012-01-30 09:19:17]

http://codereview.appspot.com/5595043/diff/4020/input/regression/tablature-ch...
File input/regression/tablature-chord-repetition.ly (right):

http://codereview.appspot.com/5595043/diff/4020/input/regression/tablature-ch...
input/regression/tablature-chord-repetition.ly:5: to save the string
information. This setting is set as default with
Ok, I am not happy about this showing up as a change in regtests because, uh, it
is a changed regtest.

So I'll retain the old copy, mentioning that it uses a deprecated interface, and
create a new one under a different name that shows the new
functionality/interface.

Is that the way to do it?