Generalize the parsing of log files

The code is pretty much the same, except the cclib parser
used depends on the type of log file. This calls for the
parser from the relevant subclass.
Creating more general parsers for various file types

There are cases where we want to translate Mopac geometries
and use them in Gaussian calculations. These parsers have to
be available to both methods so they're written here. The
alternative would be code repetition.
Have mopac double-ended methods use general parsers