Pyvibdmc

Continuous weighting fix for imp sampling and efficiency increase in discrete weighting imp samp.

Previously, `PyVibDMC` file output was in atomic units, but any analysis or reading of that data was done in angstroms or cm-1. Now, the output has remained in atomic units, and the analysis code is by default still in atomic units. One can pass in an optional keyword argument in order to convert the output to angstroms/cm-1.

NOTE: This is not a backwards compatible change. Please be careful of loading in old data or using old code, now the default is atomic units for everything.

**Full Changelog**: https://github.com/rjdirisio/pyvibdmc/compare/1.2.3...1.3.0

Made Chain rule more efficient. Based on how it is currently structured, one can now reuse derivatives that have already been calculated.

In this release, the use of guiding functions is incorporated into the DMC simulation. The guiding functions have multiprocessing and MPI support and use a similar interface as the potential manager. See updated documentation.

The `mass` argument couldn't take numpy arrays (only lists), now that is supported.

When the simulation encounters an error on the Python side, it now prints that it encountered an error. Still checkpoints and then completes the simulation.

CI changed to be more robust.

MPI parallelization was added for potential calls through `MPI4Py`. Molecular descriptors for NN-DMC were formalized in this version, and they are documented now. Users are also now allowed to add `additional_timesteps` to their DMC simulations, and there will always be a checkpointed file at the end of the simulation. Users may also extract the `vref` array as well as the walkers from the checkpointed DMC object.