* lily/prob-scheme.cc (LY_DEFINE): new file.

* lily/prob-scheme.cc (LY_DEFINE): new file.
(LY_DEFINE): functions ly:make-prob , ly:prob-type? , ly:prob-(set-)property(!)

* lily/music-scheme.cc (LY_DEFINE): rewrite get/set property using
prob functions.

* lily/music.cc (derived_mark): derive Music from Prob.

* lily/paper-system.cc (LY_DEFINE): derive from Prob.

* lily/prob.cc (Module): Implement Prob (Property Object), object
with shared and r/w property alists.

* lily/include/prob.hh (Module): new file. Declare Prob.