* ly/music-functions-init.ly (def-music-function): new helper

* ly/music-functions-init.ly (def-music-function): new helper
macro for defining music functions. \addlyrics \appoggiatura
\acciaccatura \grace \partcombine \autochange \applycontext
\applyoutput and \breathe are now defined here thanks to it.

* lily/parser.yy:
* lily/my-lily-lexer.cc: \addlyrics \appoggiatura \acciaccatura
\grace \partcombine \autochange \applycontext \applyoutput and
\breathe keywords removed from the parser.

* lily/parser.yy:
* lily/music-function.cc (ly_make_music_function):
* lily/lexer.ll (music_function_type): added a case for 0-arg
music functions.