Stef Smeets

3D periodic meshing would be useful long-term to speed up long running calculations. Needs a proof of concept in 2D first: #86

Instead of an empirical definition of the free energy from the trajectory, which depends on the quality of the MD simulation, it is possible to implement a more statistical approach....

This PR fixes some mypy issues.

Instamatic has types in quite a few places already, add type checking using mypy. There are currently over 700 issues though, but at least mypy could help make the code...