Ebcc

What's Changed
* Degenerate spin permutation simplifications
* Disable 3.7 tests, add 3.10 and 3.11
* Changes to einsum
* Support for saving and loading calculations

This release also triggers publishing, for now on TestPyPI.


**Full Changelog**: https://github.com/BoothGroup/ebcc/compare/v1.1.0...v1.2.1

What's Changed
* Adds CCD (R, U, G)
* Adds QCISD (R, U, G)
* Adds CCSDTQ (g)
* Adds Brueckner orbital self-consistency
* Optimises CC2, CCSD(T) codes

What's Changed
* Active, inactive and frozen spaces now supported
* Improved ansatz input syntax
* Optimisations to CCSD, CC2 and CC3

Initial release of `ebcc`.