Added Gutenberg link

Gutenberg includes Beethoven quartets, Haydn, Mozart, and others in xml
format
more getElementsByOffset tests
stream.timespans: lack of beatStrength don't fail

added try, except to beatStrength
update xlrd to 0.9.3 (Py3 compat)
better commits for xlrd...
fix suggested by Sarig Sela
updated iPython settings.
added omr package -- correct and evaluate OMR
updated copyright on omr.evaluators
evaluators autoCorrelate -- better
documented includeElementsThatEndAtStart
Documented more timespan methods.
Wrote more timespan documentation.
omr, enum, timespan small changes

added ext/enum34 package. Typo fixes to timespans, code review on
theoryAnalyzer. OMR rename of SingleScore
omr refactor; stream measures bug fix.
fixed xmlHandler testExternal
VLQ.MotionType is now an Enum (Str)
converter.py to converter; subconverters

Removed intermediate pickling from MusicXML (not needed). Speed up
layout.py now that it’s stable.
converter now uses sub converter for more
switched .write to subconverters

.show will be next