Python-ly

- Improvements:
- added LilyPond 2.20 words (PR140 by Simon Albrecht)
- Bugfixes:
- Fixed 144 Error when making rhythm implicit per line

- Various improvements to the experimental MusicXML output
- Fixed 32 Correctly export measures without the help of explicit barchecks
- Fixed 102 MusicXML: \mark is not exported
- Fixed 107 MusicXML: scale_rest bug
- Fixed 110 MusicXML: stem direction is not supported
- Fixed 114 Empty measures created with no attributes
- Many improvements by Felippe Roza, Peter Bjuhr, Urs Liska, Endre Oma and
others, thanks!
- Fixed Frescobaldi1213 eps-file -> epsfile
- improved indentation of Scheme code, thanks to Paul Morris (132)

- basic support for tokenizing the MUP format
- fix wbsoft/frescobaldi832: wrong duration handling with \partial when
changing durations
- xml export tests now work correctly with Python3
- fix 74 traversing events fails in empty \alternative

- support LilyPond 2.18+ behaviour on \relative without startpitch in
the ly.pitch.transpose, ly.pitch.rel2abs and ly.pitch.abs2rel modules.
- support LilyPond 2.18+ behaviour on \relative without startpitch in the
transpose, rel2abs, abs2rel and musicxml ly commands. Two new variables
were added to influence the behaviour: rel-absolute and rel-startpitch.
- add Simplifier transposer and simplify-accidentals ly command (40)
- make define-markup-command recognition working again
- recognize \bookOutputName A (without quotes, although not recommended)
- allow multi-digit fingering, e.g. c-34, LilyPond supports that since at least
2.16.
- various updates and improvements in MusicXML export contributed by Peter Bjuhr
- added ly-server: an HTTP-server for manipulating LilyPond source, contributed
by Urs Liska
- fix issue 56: do not add durations to bass notes in chordmode
- fix issue 59: handle \include commands correctly when exporting to MusicXML

- Fix issue 35: do not insert duration after a tie
- Added ly.rhythm.music_items() for a more robust way of iterating through
chords and notes (awaiting fully fledged editing support through ly.music or
ly.xml)
- More configurability in ly.colorize, thanks to Urs Liska
- MusicXML export various improvements and bug fixes, contributed by Peter Bjuhr

- add the default-language variable to the ly command; this can be set to a
language in case a LilyPond document uses a language different than
"nederlands" but does not specify it (issue 20).
- add the -l, --language option as shorthand for setting the default language
- properly support drum notes in ly.lex and ly.music
- updated scheme variables in ly.data.scheme* functions for LilyPond 2.18
- fix TypeError: expected string or buffer in dom.ly when string was a
dom.Reference (issue wbsoft/frescobaldi667)
- Fix issue 16: Duration after `\skip` may not be removed
- MusicXML export improvements:
- support for isolated durations (a single duration without
explicit pitch)
- support for implicit starting pitch in relative mode
(issues 18 and wbsoft/frescobaldi648)