Implement i-EIP method

[shoubhikraj]

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Checklist

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

[codecov[bot]]

Codecov Report

Merging #299 (b8cf727) into v1.4.1 (86a8109) will increase coverage by 0.03%. Report is 2 commits behind head on v1.4.1. The diff coverage is 98.73%.

@@            Coverage Diff             @@
##           v1.4.1     #299      +/-   ##
==========================================
+ Coverage   97.33%   97.36%   +0.03%     
==========================================
  Files         203      206       +3     
  Lines       22445    22957     +512     
==========================================
+ Hits        21846    22352     +506     
- Misses        599      605       +6     

Flag	Coverage Δ
unittests	97.36% <98.73%> (+0.03%)	:arrow_up:

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

Files Changed	Coverage Δ
autode/bracket/base.py	96.00% <ø> (ø)
autode/config.py	100.00% <ø> (ø)
autode/bracket/ieip.py	97.76% <97.76%> (ø)
autode/thermochemistry/igm.py	99.40% <98.64%> (+0.14%)	:arrow_up:
autode/path/interpolation.py	98.82% <98.82%> (ø)
autode/bracket/imagepair.py	98.81% <100.00%> (ø)
tests/test_bracket/test_ieip.py	100.00% <100.00%> (ø)
tests/test_path.py	100.00% <100.00%> (ø)
tests/test_thermochem.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[shoubhikraj]

@t-young31 Happy for you to check this again, or merge if everything is fine