added spin adapted UMP2 to psi4numpy

[mdav2]

Description

Adds an example spin adapted UMP2 code to psi4numpy. I ran into a few glitches learning how to spin adapt MP2 and CCSD, and would have liked to have a reference code to compare notes against. So, this PR is intended to fill that gap.

What are your new additions? Please provide a brief list.

• New Features

  • [x] New spin adapted UMP2 code example.

• Changes

  • [x] Add UMP2_Spin_Adapted.py

• Questions I'm not sure if the style is up to snuff, so I'll change anything that is noted.

[codecov-io]

Codecov Report

Merging #90 into master will not change coverage. The diff coverage is n/a.

[mdav2]

Can I get a second review/merge if it all looks good?

[dgasmith]

Thanks for the new tutorial! Everything looks fantastic.