Buffix: issues continuing of not converged

• There was an error continuing if the user requested to continue if the optimization did not converge.

Improved citation handling

Merge pull request #2 from molssi-seamm/dev

Improved citation handling

Added various convergence metrics to results

• Added maximum force, gradient, etc. to results.
• Improved control over when to calculate the Hessian matrix.
• Fixed an issue converting the units of the gradients.

Initial release

Working, and tested, reasonably well.