Added more atom typing for OPLS-AA
Added typing for the following functional groups, which were missed in the first implementation.
- cyclopropane -CH2-, -CHR-, and -CR2-
- hexafluorobenzene
- difluorobenzene
- bromobenzene
- iodobenzene
- thiophenol
- alkyl nitriles
- nitroalkanes
- nitrobenzene
- methylene in phenylacetonitrile
- corrections to methylene nitrile anion