`astartes` Minor + Patch Release 1.2.1

This release is a combination of 1.2.0 (which was yanked due to a bug) and 1.2.1 (which fixes the bug) - new features include the TargetValue and MolecularWeight samplers and some minor formatting and bug fixes elsewhere. Try out the new samplers to see how well your model can extrapolate outside of the training target space!