Fix the drawing of some molecules with the incorrect aspect ratio.

Also update the comments in the rdkit drawing code.
Closes #139
Signed-off-by: Richard West <r.west@neu.edu>
Tweak the logic node parsing.

I think this is correct. It may have been OK before, but I made this change on
another branch. One change or the other is needed to make it cope with node names
containing "OR".
Match truncated InChI from MOPAC logfiles due to MOPAC2012 bug.

MOPAC2012 deletes 81st character from InChI string in input file, leading
to some mismatches.  Use only up to the first 80 characters to match to
the InChI (at least until they fix this bug.)

See https://github.com/GreenGroup/RMG-Py/issues/137 for more details.