* flower/include/offset.hh (class Offset): new operator /=

* flower/include/offset.hh (class Offset): new operator /=

* lily/tuplet-number.cc (print): new file, new interface.

* scm/define-grob-properties.scm (all-user-grob-properties):
remove number-visibility property.

* lily/tuplet-bracket.cc (calc_control_points): new function
(calc_connect_to_neighbors): new function.
(print): remove text handling for tuplet numberdef.

* lily/tuplet-engraver.cc (struct Tuplet_description): create
TupletNumbers too.

* lily/lily-guile.cc (robust_scm2booldrul): new function

* scm/define-grobs.scm (all-grob-descriptions): new grob TupletNumber

* lily/tuplet-bracket.cc (calc_position_and_height): use
staff-padding to control whether tuplet brackets are over staves.