Low code coverage

[AntObi]

The code coverage for SMACT can be reviewed here: https://app.codecov.io/gh/WMD-group/SMACT/tree/master/smact

I would like to bring particular attention to the following modules:

module	coverage (%)
smact.distorter	23.53
smact.lattice_parameters	27.93
smact.structure_prediction	62.50
smact.properties	67.31

These modules (the first two in particular) have particularly low coverage. I'll assign increasing the code coverage of the structure_prediction and smact.properties to myself. For the other two modules, I can look to increase the code coverage of them, but I also think that we should have a review of the codebase to see how older functions still integrate with the rest of SMACT.