Raster extension

[emmanuelmathot]

Description:

Implements the raster extension

PR Checklist:

• Code is formatted (run scripts/format)
• Tests pass (run scripts/test)
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Merging #364 (be2e41c) into main (e90f809) will increase coverage by 0.02%.
The diff coverage is 90.21%.

@@            Coverage Diff             @@
##             main     #364      +/-   ##
==========================================
+ Coverage   89.77%   89.80%   +0.02%     
==========================================
  Files          37       38       +1     
  Lines        4677     4953     +276     
==========================================
+ Hits         4199     4448     +249     
- Misses        478      505      +27     

Impacted Files	Coverage Δ
pystac/extensions/raster.py	90.21% <90.21%> (ø)

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[duckontheweb]

Thanks for this @emmanuelmathot. I added some suggested changes to bring the docstrings in line with some changes from recent PRs.

We should also add the classes from pystac.extensions.raster into the API docs by adding them to docs/api.rst.

[emmanuelmathot]

Thank you @duckontheweb for the review!