clarify information about dependencies

- pip can only install Python modules
- add pyPdf and midi to the list
- cover exact versions tested
ignore build/ and src/
fix typos
add --keep to keep temporary files for debugging
avoid starting on page 10 if we have >= 10 pages

https://github.com/aspiers/ly2video/issues/8
remove pointless code following fatal() invocation
trim fat from warning/error messages and reuse fatal() where appropriate
use Pythonic string interpolation
print a dot for every 10 frames rendered
replace linkLy[n] with intuitive variable names
fix indentation
watch for char != column to try and understand when these would be different
separation of notes from ties and merging near indices happens in the same pass
extract getNotePositions() function for legibility
extract separateNotesFromTies() for legibility
extract compareIndices() for legibility
extract parseOptions() for legibility
extract findExecutableDependencies() and portableDevNull() for legibility
extract getCursorLineColor() and rename color variable for legibility
extract getResolution() for legibility