Update master to main and other modernizations

[kaosine]

I'm proposing these changes as updates and modernizations going forward:

1. Naming schemes have changed since master was the default, I propose changing master to main or some other form of this.
2. Clean up the tags into releases if possible, while making the new tags x.y.z in such a form that if it's <1.0 tag it as 0.x, >1 tag as 1..y. Just for clean up purposes to make things clearer going forward. Especially since the UI in GitHub prioritizes releases over tags in showing that a recent release has happened. That way it's easier to know what has been touched recently and what hasn't beyond just commit dates. Since those aren't always reliable on determining if the project is still active.
3. Also, with having atom-community(atomic) on the org home, I recommend changing it to just atomic and reflecting that branding elsewhere throughout the org. The current name is too long, and with upstream's sunset, the simpler name seems like a good choice going forward. Especially since that seemed to be the original intention naming wise but was abandoned for a whatever reason.

[ghost]

"atomic rebrand"? Why? People who don't notice that Atom community is aka Atomic, it will be like "WHAT'S Atomic?".

[ghost]

"cleanup tags"? There are LOTS! It will take around ~15-25 minutes to do that.