* scm/music-functions.scm (skip-to-last): new function. Show only

* scm/music-functions.scm (skip-to-last): new function. Show only
last showLastLength part of the \score.

* lily/moment-scheme.cc (LY_DEFINE): new function ly:moment-sub

* python/convertrules.py (conv): add ly:x-moment rule

* lily/moment-scheme.cc (LY_DEFINE): rename ly:X-moment  -> ly:moment-X

* Documentation/topdocs/NEWS.tely (Top): add new feature.

* Documentation/user/instrument-notation.itely (Flexibility in
alignment): options in subsections.

* lily/lyric-engraver.cc (process_music): don't typeset text for _
syllable text. Instead, assume that the previous lyric text is a
melismated text.

* Documentation/index.html.in: revert 800x600 change.