Seamm-util

* added e.g. eV*Å^6 to kcal/mol*Å^6 to support Buckingham pontetials

* To make the schema-type JSON more human-readable.

* Added energy/mol/Å^2 --> energy/Å^2 for force constants
* Added energy/mol/Å^3 --> energy/Å^3 for stress/pressure/elastic constants

* First release on PyPI.