initial pass at ZBO support.
does not yet handle the HYD and ZCH lines
stop messing up aromaticity and hybridization;
all tests pass, but this is definitely not the most efficient thing.
merge
add support for the ZCH and HYD elements in mol files
initial version from Jan Holst Jensen
minor updates
add to python wrapper
add some tests; add radicals to output
get rgroups working
a few more tests and a fix to not print empty bond blocks
fix isotope handling in V3K
get atom lists working
support forcing V3000 writing and kekulization in the SDWriter
Fixes #174
add tests for the kekulize and forceV3000 options
a couple more tweaks from Jan
add (non-standard) handling of R groups to v3k mol parser
more isotope fixing
further R group handling
Fixes #187
Fixes #186