Replace use of pkg_resources with importlib.metadata

[jschwartzentruber]

Fixes #98

[codecov[bot]]

Codecov Report

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

Project coverage is 83.31%. Comparing base (823ca21) to head (0ee7fd9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #99 +/- ## ========================================== + Coverage 83.25% 83.31% +0.05% ========================================== Files 13 13 Lines 1463 1468 +5 ========================================== + Hits 1218 1223 +5 Misses 245 245 ```

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