* lily/include/beam.hh: new struct, softcode beam quanting parameters

* lily/include/beam.hh: new struct, softcode beam quanting parameters

* lily/include/grob.hh (class Grob): add interfaces_ member.

* lily/bezier.cc (init_polynomial_cache): new function: cache
binom(3,j) t^j (1-t)^{3-j}
(curve_point): opps, actually use the cache for t^j , (1-t)^j!

* lily/grob-property.cc (internal_get_object): new routine.
(internal_set_object): idem. Store grob refrences in separate
alist. This saves processing time, since properties aren't
break-substituted, and the per grob namespace is smaller, both for
grobs and non-grob properties.

* scm/define-grob-properties.scm (all-internal-grob-properties):
remove center-element.

* lily/grob.cc: remove tweak-count, tweak-rank.