Re: Issue 3926: Add \magnifyMusic; clarify fontSize in docs. (issue 96570043)

[markpolesky]

I've uploaded a new patch set, with the following changes:

1) horizontal spacing now scales along with the resizing
2) \magnifyMusic now takes a music block, so that
   -- the temporary overrides can revert automatically
   -- the user doesn't need to manually reset it to 1
3) updated font-size description in define-grob-properties.scm
4) added regtest
5) mention \magnifyMusic in changes.tely
6) updated documentation accordingly

By the way, about the linear interpolation on the beam-thickness value,
the results look good to me across the board; here is the regtest png:
http://bit.ly/1pnVozg

Sorry I didn't think of these changes before my first upload.  Please
review the new patch.

Thanks!
- Mark

https://codereview.appspot.com/96570043/