Add colorize and palettize to XRImage enhancement_history

[djhoese]

I'm 90% sure of the logic on this, but would appreciate a double check. I would like this functionality for my own scripts in my Polar2Grid and Geo2Grid projects. With this the geotiff scale and offset metadata values include the range of the colormap used in palettize or colorize. I can then use that to determine the min/max of the original data so a colorbar can be added (with pydecorate) with the correct limit labels.

• Closes #xxxx (remove if there is no corresponding issue, which should only be the case for minor changes)
• Tests added (for all bug fixes or enhancements)
• Tests passed (for all non-documentation changes)
• Passes git diff origin/master **/*py | flake8 --diff (remove if you did not edit any Python files)
• Fully documented (remove if this change should not be visible to users, e.g., if it is an internal clean-up, or if this is part of a larger project that will be documented later)

[codecov]

Codecov Report

Merging #99 (ecb7632) into main (4c1bc5b) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
+ Coverage   92.21%   92.26%   +0.05%     
==========================================
  Files          10       10              
  Lines        3389     3411      +22     
==========================================
+ Hits         3125     3147      +22     
  Misses        264      264              

Flag	Coverage Δ
unittests	92.26% <100.00%> (+0.05%)	⬆️

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Impacted Files	Coverage Δ
trollimage/tests/test_image.py	99.92% <100.00%> (+<0.01%)	⬆️
trollimage/xrimage.py	87.96% <100.00%> (+0.17%)	⬆️

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[pnuu]

Just one comment, otherwise LGTM.

[pnuu]

LGTM