[Improve] Choose `experimental` or `preview` branch (for duration where some of this is unfinished but some of this has use)

[SwuduSusuwu]

Rationales:

• This (git clone https://github.com/SwuduSusuwu/SubStack.git, which defaults to the trunk branch) has numerous subjects/tools, thus expect sizable duration whereupon: some of those tools are unfinished, but some are finished or have use.

Background:

• To address this, the experimental branch (git switch experimental) was produced (whose full logs exist at https://github.com/SwuduSusuwu/SubStack/activity?ref=experimental , with normal git log at https://github.com/SwuduSusuwu/SubStack/commits/experimental).
  • But its purpose is more about a stable git log (the goal is to just use git rebase && git push --force with the experimental branch from now), so that  git pull --rebase is not required or the trunk branch: the trunk branch has published numerous (unfinished) tools.

[SwuduSusuwu]

The purpose was to use experimental as a continuous integration branch, so that trunk would not have rebases.
Got a few commits fit to use for trunk, GitHub kept suggesting to do a pull request and said it would replay (not merge) the commits, but it created a diverged tree (unrelated commit hashes) filled with conflicts so that there was no choice but to git push --force to undo.
Will just commit through git push from now on (since GitHub cannot fastforward.)
If you had the misfortune to git pull after this happened but before this was fixed, you must git pull --rebase.

[SwuduSusuwu]

PR #32 PR #33 are examples of how this should go (GitHub marks pull requests as merged once the request's individual commits are git pushd into trunk branch).

[SwuduSusuwu]

Notice: is possible that in the future, will rename this branch to preview.

• For now, preview just acts as a mirror for this branch while this branch is in the middle of a partial merge (which, for GitHub pull requests, requires to roll this branch back to the last commit which will merge).
  • The effect is that the preview branch exists and has the most new version of code, but is unofficial for now.