ENH: Improvements to DFTB+ I/O
Added ability to read the GenFormat geometry block from the dftb_in.hsd file.
Additionally, DFTB+ calculates the stress tensor; however the stress is not read in by the calculator. I have added "stress" to the "implemented_properties" list and added in the functionality to read in the stress from "results.tag". In doing so, I made several efficiency changes to how this file was parsed.
Finally, pep8 and pyflakes revealed several stylistic changes that were required, and they were addressed.