Deal properly with multiple molecules with multi-line properties.

per discussion on the list under "obabel: Converting sdf with multi-line properties" and
suggestion from Chris Morley.
Merge pull request #79 from jeffjanes/multiline

Deal properly with multiple molecules with multi-line properties.
Add template for RN-CN2 guanidine bond typing.
Force field updates.

Make MMFF94 the default force field for everything (about time)
A variety of other minor fixes.
OBDepict: Draw aromatic rings first to ensure all double bonds are
inside an aromatic ring.