PM6

PM6 method added to QMthermo. It is currently implemented such that users only have a choice between pm3 and pm6 (easy to add a few more if desired). The original thought behind limiting the number of methods was to foster the sharing of output files (this idea hasn't really taken off). This would be more difficult if the user had an unrestricted choice of methods and basis sets used in QMthermo.

On the other hand it is probably more desirable for the user to have those options. The implementation will have to be tweaked to allow this, but shouldn't be too bad. I foresee problems when using files from previous jobs. QMthermo currently doesn't check method consistency (method used in an old log file the same as the current job) as they all were pm3 before this change.

I'm not sure which is better. Having the choice is nice but introduces other issues not previously considered in the qm module.