Rename "master" branch to "main"?

[Florian Weimer]

* Zack Weinberg:

> That said I think this is not as important as other, similar, changes
> we could make.  For instance, the term "master" is used _along with_
> "slave" in manual/terminal.texi, and I fully intend to rewrite that
> chapter to eliminate that terminology as soon as I find the time.
> Anyone want to beat me to it?

We need some term that starts with “s”, to maintain the connection with
/dev/pts and ptsname (and maybe others).  So far, I've come up with
“surface”, because that's where terminal data is written and read.  It
certainly seems more descriptive than “slave”.  But perhaps there is a
better alternative.

Thanks,
Florian