Preparing for v3.0.0 Release

[desilinguist]

This PR closes #701 and closes #710.

• Update version number.
• Update conda recipe. Make it a noarch recipe again based on the conda-forge recipe. Remove conda_build_config.yaml since we don’t need it anymore. Also update the conda-recipe README.
• Drop Python 3.7 from the README and from setup.py.
• Use Python 3.8 for ReadTheDocs builds as well.

The conda package has been uploaded to the ets channel. The source tarball has also been uploaded to the test.pypi.org. See passing builds on Linux and Windows for both packages below.

• Conda Package

  • Linux Build (Python 3.8)
  • Windows Build (Python 3.10)

• TestPyPI Package

  • Linux Build (Python 3.8)
  • Windows Build (Python 3.9)

Please test both the packages on macOS and look at the drafted release notes as part of reviewing this PR.

[codecov[bot]]

Codecov Report

Merging #711 (c02377b) into main (61bef9c) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #711   +/-   ##
=======================================
  Coverage   96.90%   96.90%           
=======================================
  Files          63       63           
  Lines        9263     9263           
=======================================
  Hits         8976     8976           
  Misses        287      287           

Impacted Files	Coverage Δ
setup.py	0.00% <ø> (ø)
skll/version.py	100.00% <100.00%> (ø)

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