Missing sqlalchemy operators

[JakNowy]

This implements #79 by introducing FastCRUD._get_sqlalchemy_filter() method and a dictonary of filter mappings in FastCRUD._SUPPORTED_FILTERS. Adding new sqlalchemy opertors is as simple as extending the dictonary.

It also solves the or_() operator issue:

                    ItemCRUD.get_multi(
                        name__or={'startswith': 'foo', 'endswith': 'bar'}
                    )

There is some mypy issue which I struggle to solve, but it looks like it's not required. The tests pass with good coverage.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (03d4a2d) to head (f8f8713). Report is 16 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #85 +/- ## ========================================== Coverage 100.00% 100.00% ========================================== Files 68 70 +2 Lines 4819 5425 +606 ========================================== + Hits 4819 5425 +606 ```

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[JakNowy]

@igorbenav this is ready for review. I'm going to add some docs tomorrow.

[igorbenav]

I think all that's missing are typing fixes and docs and we're good to go

[JakNowy]

@igorbenav Added docs and fixed checks. The latest commit makes the code a bit less clean, but it satisfies mypy, it's up to you if you want to keep it. Let me know your thoughts!

[igorbenav]

Looking really good, @JakNowy, great work!