1. Only show tune markers when a tune change is in the middle of a line.
2. Only show repeat starts |: if the repeat start is in the middle of a line.
3. Final bar end mark must be a thick line.
The official rules for a repeat are that if there is no left repeat
marker |: then the repeat starts at the previous double bar.
Currently we rely on any N: field with a Change: subnotice being the first
N: field. Add --contains field to abcfield.py to remove this restriction.
Also use it to extract new subfield Credit: and add that if present
to the tune information in print and on web.
Jim Hague
Jim Hague