* lily/beam.cc: use length-fraction too.

* lily/beam.cc: use length-fraction too.

* lily/beam.cc: remove flag-width-function

* lily/stem.cc (calc_length): multiply with length_fraction. Makes
for easier grace tweaks.

* lily/beam.cc: remove dir-function.

* lily/note-head.cc (calc_stem_attachment): new function.
(internal_print): use callback to get glyph-name.

* lily/stem.cc (calc_stem_end_position): new function.
(calc_length): new function.
document details for stem.
remove Stem::get_direction()

* lily/stem.cc (height): idem.

* lily/beam.cc (calc_direction): use pseudo-property for beam
direction callback.
(calc_positions): use callback

* lily/stem.cc (calc_stem_end_position): use callback.
(calc_positioning_done): idem.
(calc_direction): idem.
(calc_stem_end_position): idem
(calc_stem_info): idem.