Add Notation appendix for context mod identifiers.

Add Notation appendix for context mod identifiers.

* Documentation/notation/notation-appendices.itely:

  add node for context modifications

* lily/context-mod.cc:

  add type predicate ly:context-mod?

* ly/context-mods-init.ly (RemoveEmptyStaves):

  add docstring via \description

* scm/document-context-mods.scm:

  new file for generating context-mod documentation

* scm/document-identifiers.scm (identifier<?):

  move to documentation-lib.scm

* scm/documentation-generate.scm:

  load document-context-mods.scm and output documentation to
  context-mod-identifiers.tely

* scm/documentation-lib.scm (identifier<?):

  moved from document-identifiers.scm so it can be used in
  document-context-mods.scm too

* scripts/auxiliar/ref_check.tely:

  exclude context-mod-identifiers.tely

* scripts/build/website-known-missing-files.txt:

  add context-mod-identifiers.tely

[Neil Puttock, 2011-07-23 20:18:52]

Hello,

This patch adds auto-generated documentation for context modifications
(currently, only \RemoveEmptyStaves).

Any context modification identifier defined in ly/context-mods-init.ly will get
an entry in the notation appendices so long as it has a \description docstring.

Cheers,
Neil

[pkx166h, 2011-07-24 10:06:15]

Passes make and reg tests.

James

[Graham Percival (old account), 2011-08-03 20:06:49]

LGTM, fantastic work as always.

[Neil Puttock, 2011-08-07 14:27:25]

On 2011/08/03 20:06:49, Graham Percival wrote:
> LGTM, fantastic work as always.

Thanks!

Pushed: 33f71ee2c062b4e377e146920ef48ea8c41d6fe8

Cheers,
Neil