* input/mozart-hrn-3.ly: Mimic Breitkopf fonts and padding.

* input/mozart-hrn-3.ly: Mimic Breitkopf fonts and padding.

* scm/grob-property-description.scm (number-threshold): Add
description.

* lily/multi-measure-rest.cc (brew_molecule): Only put number over
rest if #measures > number-threshold.  Use padding (well, fake
using it, anyway).

* scm/font.scm (make-style-sheet): New styles: mark-number,
mark-letter.
(paper20-style-sheet-alist): Add bigger bold fonts.

* lily/mark-engraver.cc (process_music): Use style mark-number or
mark-letter.