Make PyPI releases (with wheels) through GitHub Actions

[thejcannon]

This change adds a GitHub Action workflow file which is triggered on a push with a tag starting with release- which builds the sdist/wheel and publishes it to PyPI (leveraging PyPI's "Trusted Publishers" feature. Read more here).

Additionally:

• Fixes a few errors that twine was upset about regarding the long_description
• Removes the references/scripts to the manual release process.

Fixes #215

[thejcannon]

I tested this out on the master branch of my fork, where I have these changes, plus I tweaked the name to icdiff-test and also changed the workflow to upload to https://test.pypi.org.

Here's the successful run: https://github.com/thejcannon/icdiff/actions/runs/5833953023/job/15822472910
Here's the test.pypi link: https://test.pypi.org/project/icdiff-test/#files

❗ Note that you have to go to https://pypi.org and configure this workflow as a "Trusted Publisher". This page describes how to do that.

Here's a screenshot of my settings from test.pypi.org for my dry-run (when it was pending before the publish):

[thejcannon]

Please let me know any questions you have. I'd be more than willing to explain any and all of this 😄

Thanks again for your time <3

[jeffkaufman]

Thanks! Sorry for the slow responses; I've been traveling.

[thejcannon]

No worries, I appreciate you taking a look.

And speaking of looking: https://pypi.org/project/icdiff/#files looks great!!

Thanks again