switch primary branch from `master` to `main`

[sbc100]

All the other repos in our ecosystem have made the switch now so its really just catchup and consistency now.

Instructions for switching to main:

1. Run git fetch to ensure origin/main is fetched.
2. Run git remote set-head origin -a
3. If you don't have any local branches you can just run:

• git branch -m master main
• git branch -u origin/main main

4. If you do have local branches you will need to re-parent each of them onto main using:

• git branch -u origin/main mybranch

[kripken]

This will be the most complex branch change we've done yet, I think, because checking out the emsdk from git is the main way users use it.

Some thoughts on a possible process:

• Add a main branch, forked from master. Do not remove master yet.
• Update docs to main, continue development there.
• Add a single new change to master, a warning shown on every invocation to switch to main (assuming that emsdk is in a git checkout, and the branch is still master). Without this, people will do git pull and silently not get updates.
• Some long time later, change that warning to an error. That will be noticed by CI and other things, that missed the warning.
• Some long time later, remove master.

Thoughts?

[sbc100]

Sounds like a good plan.