* input/regression/markup-arrows.ly: new file.

* input/regression/markup-arrows.ly:  new file.

* lily/tuplet-bracket.cc: document new behavior.

* input/regression/tuplet-broken.ly: new file. Demonstrate tuplets
with line breaks.

* scm/define-markup-commands.scm (arrow-head): arrow-head markup command.

* scm/define-grobs.scm (all-grob-descriptions): set arrows as
default

* lily/tuplet-bracket.cc: add edge-text property.
add break-overshoot.
(print): read break-overshoot.
(print): read edge-text, add stencils.

* mf/feta-arrow.mf: new file.

* mf/feta-generic.mf: add feta-arrow.