Snippet tags

[Phil Holmes]

Currently, the snippets in
http://lilypond.org/doc/v2.19/Documentation/snippets/index include the
current categories/tags:

ancient notation
chords
contexts and engravers
editorial annotations
expressive marks
fretted strings
keyboards
midi
paper and layout
percussion
pitches
repeats
rhythms
simultaneous notes
spacing
staff notation
template
text
titles
tweaks and overrides
unfretted strings
vocal music
winds
world music

However, there are a _lot_ more tags in the snippet repository (see below).
 One upshot of this is that tagging a snippet with the "wrong" tags will
prevent it appearing in the docs automatically.  Should we update the list
above to be the same as the one below?

ancient-notation
automatic-notation
breaks
chords
connecting-notes
contemporary-notation
contexts-and-engravers
devel
editorial-annotations
expressive-marks
fretted-strings
headword
keyboards
midi
paper-and-layout
percussion
pitches
preparing-parts
really-cool
really-simple
real-music
repeats
rhythms
scheme-language
simultaneous-notes
spacing
specific-notation
staff-notation
stylesheet
symbols-and-glyphs
syntax-and-expressions
template
text
titles
tweaks-and-overrides
unfretted-strings
version-specific
vocal-music
winds
workaround
world-music