Refactor deprecated pkg_resources usage

[speleo3]

• Remove deprecated pkg_resources usage
• Locate resources relative to __file__
• Support egg/zip with open_file_for_reading

[codecov[bot]]

Codecov Report

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

Comparison is base (a62e2a4) 72.98% compared to head (50f62c6) 73.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #176 +/- ## ========================================== + Coverage 72.98% 73.00% +0.01% ========================================== Files 25 25 Lines 4017 4027 +10 ========================================== + Hits 2932 2940 +8 - Misses 1085 1087 +2 ```

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[sobolevnrm]

Looks great!