Implemented aExp and bExp options

[sseraj]

Purpose

Closes #40. Please see the issue for some discussion on the performance penalty compared to hard-coded values for the exponents.

Type of change

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (non-backwards-compatible fix or feature)
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no API changes)
• [ ] Documentation update
• [ ] Maintenance update
• [ ] Other (please describe)

Testing

I plan to add a test with non-default exponents in a subsequent PR where I will add a test for MultiUSMesh.

Checklist

• [x] I have run flake8 and black to make sure the code adheres to PEP-8 and is consistently formatted
• [x] I have run unit and regression tests which pass locally with my changes
• [ ] I have added new tests that prove my fix is effective or that my feature works
• [x] I have added necessary documentation

[codecov[bot]]

Codecov Report

Merging #64 (9618729) into master (5656b04) will decrease coverage by 1.01%. The diff coverage is n/a.

:exclamation: Current head 9618729 differs from pull request most recent head 93dc612. Consider uploading reports for the commit 93dc612 to get more accurate results

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
- Coverage   45.80%   44.78%   -1.02%     
==========================================
  Files           6        6              
  Lines         751      748       -3     
==========================================
- Hits          344      335       -9     
- Misses        407      413       +6     

Impacted Files	Coverage Δ
idwarp/UnstructuredMesh.py	60.99% <ø> (-0.04%)	:arrow_down:
idwarp/UnstructuredMesh_C.py	46.15% <0.00%> (-53.85%)	:arrow_down:

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[marcomangano]

As discussed during the maintenance meeting, a test will be added in an upcoming PR

[ewu63]

@eirikurj @SichengHe could you take a look at this some time? It would be really helpful to get this feature merged.

[joanibal]

@SichengHe @eirikurj. Just another reminder, as I would also like to get this feature on the main branch ASAP