Issue 4015: Add \magnifyStaff. (issue 117830043 by address@hidden)

[markpolesky]

Reviewers: ,

Message:
Here's a new music function called \magnifyStaff (along the lines of
\magnifyMusic) that scales staff sizes, staff lines, bar lines,
beamlets, and horizontal spacing at the Staff context level.  Staff
lines are prevented from being scaled smaller than the default (and
consequently, so are stems, slurs, etc., since the thickness of each is
based on staff lines).  This should improve the user experience for this
task, which is somewhat cumbersome as it stands.

I rewrote the backend to \magnifyMusic so that the two functions could
share some code.  The bulk of the code is in:
  ly/music-functions-init.ly
  scm/music-functions.scm
  scm/define-context-properties.scm

You can see example usages in the modified Documentation files and
regtests.

This is issue 4015 on the tracker:
http://code.google.com/p/lilypond/issues/detail?id=4015

Cheers,
Mark

Description:
* Add \magnifyStaff.
* Rewrite parts of the \magnifyMusic function so that it can share
  some scheme code with the new \magnifyStaff function.
* Add regtests.
* Update documentation.

Please review this at https://codereview.appspot.com/117830043/

Affected files (+329, -95 lines):
  M Documentation/essay/engraving.itely
  M Documentation/music-glossary.tely
  M Documentation/notation/spacing.itely
  M Documentation/notation/staff.itely
  A input/regression/magnifyStaff-bar-lines.ly
  A input/regression/magnifyStaff-dots-beamlets.ly
  A input/regression/magnifyStaff-space-alist.ly
  A input/regression/magnifyStaff-staff-line-thickness.ly
  M ly/music-functions-init.ly
  M scm/define-context-properties.scm
  M scm/music-functions.scm