Add a solve_fermion function for compatibility with SQD

[caleb-johnson]

Fixes #24

This PR adds a function, solve_fermion, to mimic solve_fermion in SQD.

Key deviations from original function:

• Make a working directory in the system's temp directory if one isn't specified
• Create an fci dump from the integrals.
  • SInce we do this, we can ensure there is no nuclear repulsion energy in the fci dump, so we don't have to account for it (same as SQD)
• Takes a bitstring matrix, rather than addresses. Does not accept addresses as a deprecated arg.

TODO:

• Release note