Minenkov thermochem

[t-young31]

Resolves #289

Adds the suggested method and tidies up the igm module. There's much more that could be better but 🤷🏼, at least it's better than it was.

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Checklist

• The changes include an associated explanation of how/why
• Test pass
• Documentation has been updated
• Changelog has been updated

[codecov]

Codecov Report

Merging #292 (6678f2d) into v1.4.1 (86a8109) will increase coverage by 0.00%.
The diff coverage is 98.86%.

❗ Current head 6678f2d differs from pull request most recent head a81ba1a. Consider uploading reports for the commit a81ba1a to get more accurate results

@@           Coverage Diff           @@
##           v1.4.1     #292   +/-   ##
=======================================
  Coverage   97.33%   97.33%           
=======================================
  Files         203      203           
  Lines       22445    22490   +45     
=======================================
+ Hits        21846    21891   +45     
  Misses        599      599           

Flag	Coverage Δ
unittests	97.33% <98.86%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
autode/config.py	100.00% <ø> (ø)
autode/thermochemistry/igm.py	99.40% <98.64%> (+0.14%)	⬆️
tests/test_thermochem.py	100.00% <100.00%> (ø)