Update links to point main branch of ml5-library & remove references to ml5-examples

[bomanimc]

This PR has a few focuses:

• Removing references to the release and development branches in ml5-library, and point them to the new main branch will be our prevailing "source of truth" for the latest, released code in ml5.js after the release of 0.6.0. https://github.com/ml5js/ml5-library/issues/917
• Cleaning up all of the references to ml5-examples that were leftover from our archival of that repository. I accidentally forgot to clean these up after the transition.
• Replace references to https://ml5js.github.io/ml5-examples to https://examples.ml5js.org, so that these links aren't dependent on our GitHub pages hosting now that we've moved over to Netlify.
• I also made some small changes to the "Running Examples" docs to make note of the newer npm run develop command I added earlier this year.