Issue 3799: New satb.ly built-in template and template framework (issue 225860043 by address@hidden)

[tdanielsmusic]

Reviewers: ,

Message:
This patch is posted for comment and improvement rather than a candidate
for immediate inclusion in the code base.  Some
caveats/issues/questions:

\includes are used for testing; later, perhaps after settling on the
file names, these may not be necessary.

Indenting is problematic, due to the heavy mixing of Scheme and Lily
code.

base-tkit.ly is actually pure Scheme, and perhaps should be recast as
base-tkit.scm and located elsewhere.

There are no regression tests and no documentation at present.  These
would need to be added.


Description:
Issue 3799: New satb.ly built-in template and template framework

  Add kits as aids for providing built-in templates ("tkits")

  Replace the satb.ly template with one built from the tkits, which
  corrects some errors and extends the facilities:
    - fixes issue 4192
    - Women and Men one-voice staves added
    - Soprano and Tenor music may now be omitted without error
    - midi instruments may be specified
    - midi channel mapping is by instrument
    - midi instruments are by voice, not staff

Please review this at https://codereview.appspot.com/225860043/

Affected files (+548, -183 lines):
  A ly/base-tkit.ly
  A ly/lyrics-tkit.ly
  A ly/piano-tkit.ly
  M ly/satb.ly
  A ly/staff-tkit.ly
  A ly/vocal-tkit.ly
  A ly/voice-tkit.ly