Update README and home page of the docs

[drbenvincent]

Partially addresses #422

For both the GitHub README, and the docs home page this PR:

• Removes the images from the Features section. Also removes their source files, and the notebook that generated them.
• Replaces that section with a table of the various methods / quasi-experimental designs.

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📚 Documentation preview 📚: https://causalpy--423.org.readthedocs.build/en/423/

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.40%. Comparing base (d31a033) to head (f479100).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #423   +/-   ##
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  Coverage   94.40%   94.40%           
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  Files          31       31           
  Lines        1985     1985           
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  Hits         1874     1874           
  Misses        111      111           

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[juanitorduz]

Regarding the PR itself it looks good.

Still, personally, I think I like the plots more, but this is just my personal opinion. The table is also good :)

[drbenvincent]

I know what you mean, but it started to feel cluttered.