Add image sharpening algorithm

[harshitpant1]

Description

Image sharpening is a practice used frequently in fields like astronomy, printing industries and many other areas of image processing. This PR adds image sharpening functionality (using unsharp masking algorithm) for grayscale and RGB images to GIL.

References

Principles of Digital Image Processing: Fundamental Techniques by Wilhelm Burger, Mark J. Burge.

Tasklist

• Add test case(s)
• Ensure all CI builds pass
• Review and approve

[harshitpant1]

Note that for this to work, #577 needs to be looked into first.
Gentle reminder to @lpranam

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.28%. Comparing base (4d97acb) to head (cb90d78).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #584      +/-   ##
===========================================
+ Coverage    82.05%   82.28%   +0.23%     
===========================================
  Files          117      118       +1     
  Lines         5383     5453      +70     
===========================================
+ Hits          4417     4487      +70     
  Misses         966      966              

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[sdebionne]

Added two regression tests (spike_produces_halo, threshold_suppresses_weak_edge) that assert on concrete sharpened output rather than degenerate no-op inputs.

[sdebionne]

@mloskot I will update the documentation once it is in AsciiDoc (to avoid reconverting again). MrDocs is getting a fix for the GIL headers 👍 .

[mloskot]

Yeah, I've seen the comments. Funny, I've been disconnect from Boost for so long that I didn't know about the MrDocs thing. Thanks @sdebionne !