Adding a function to perform mesh generation only. Adding ability to combine input filles in the PyGriffin.run method.

Adding contribution guide.

See merge request nstauff/PyGriffin!5

Update configuration and tests

See merge request nstauff/PyGriffin!4

Initial input

See merge request nstauff/PyGriffin!3

Griffin wrapper code

See merge request nstauff/PyGriffin!2

Infrastructure

See merge request nstauff/PyGriffin!1