Creating a maintenance branch

If we were to follow CPython practice, as we try to, we would create a 
2.7 maintenance branch on GitHub and continue development of new 
features on "master". Actually, we would have done that some time ago.

I propose to do something slightly different as there are some 
complications:

 1. This is a major version change, which is a special case. (What I
    described is for when the minor version changes.)
 2. The 3.x code base starts "functionally empty", by which I mean
    Jython 2 code is present but not compiled. This may be confusing for
    anyone landing on the repo.
 3. There is a fashion now to call the default branch "main" rather than
    "master" and renaming has been facilitated at GitHub
    (https://github.com/github/renaming).

The slightly different thing I propose is:

 1. Create a branch called "main" at a point a little after 2.7.2 (and
    after recovery from the history corruption Jim spotted). This is the
    developement branch, but you have to select it specifically.
 2. After a delay, rename "master" to 2.7. (Branch "master" on your
    local repo still points to this. PRs against "master" at that point
    re-target to "2.7" and it is still the default. See link.)
 3. Once Jython 3 on "main" looks credible as an alpha, make "main" the
    default branch.

I'm saying this here in case anyone has a reason why it's terrible idea.

Jeff

-- 
Jeff Allen