* lily/include/event.hh: remove file.

* lily/include/event.hh: remove file.

* lily/parser.yy (Lily_lexer): check EVENT_IDENTIFIER using 'event
in 'types property.

* lily/music.cc (duration_length_callback): new function.

* lily/event.cc: remove file.

* lily/music-constructor.cc: remove file.

* lily/music-scheme.cc (LY_DEFINE): rename to ly:make-music

* lily/context.cc (get_grob_key): nop if use_object_keys not set.
(get_context_key): idem.

* scm/lily.scm (lambda): new option object-keys (default to #f)

* ps/music-drawing-routines.ps: remove draw_beam.

* lily/lookup.cc (beam): use round_filled_polygon() for beam.