Document interface of library

[emstoudenmire]

This PR adds documentation of which methods we may consider "interface", and thus should keep and add docstrings for, versus deprecated methods we may want to delete. Methods not in the two files interface_methods.md and deprecated_methods.md are considered internal, developer-facing methods.

[github-actions]

Your PR no longer requires formatting changes. Thank you for your contribution!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.23%. Comparing base (2f4ab3d) to head (ad1e38f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
- Coverage   73.26%   73.23%   -0.04%     
==========================================
  Files          66       66              
  Lines        3183     3183              
==========================================
- Hits         2332     2331       -1     
- Misses        851      852       +1     

Flag	Coverage Δ
docs	47.13% <ø> (-0.04%)	⬇️

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[mtfishman]

@emstoudenmire can you bump the version, fix the docs build, and format just so we can get tests passing?

Also, I noticed you are just including the function signatures in the docs. For functions that have docstrings, can you insert the docstring instead of just putting the function signature?

[emstoudenmire]

By the way, the interface page has gotten quite small... It's nice to see. Once we can build the main features back on top (assuming they aren't already) , such as BP, constructor codes (e.g. fermionic states) based on BP, and solvers, that will be a good situation.

[emstoudenmire]

Ready to merge this? Or let me know if other changes seem needed.