Added HasExtension to do a case-insensitive check for an extension (ignoring the dot).

[dennisdoomen]

Closes #28

[github-actions]

Test Results

 3 files  ± 0   3 suites  ±0   0s ⏱️ -3s
60 tests + 6  60 ✅ + 6  0 💤 ±0  0 ❌ ±0 
60 runs   - 38  60 ✅  - 38  0 💤 ±0  0 ❌ ±0 

Results for commit 68bd346. ± Comparison against base commit 08b6f7d.

[coveralls]

Pull Request Test Coverage Report for Build 16386022987

Details

• 10 of 10 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 96.226%

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Totals
Change from base Build 16273542856:	0.4%
Covered Lines:	119
Relevant Lines:	125

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💛 - Coveralls