Branching proposal for 2.7.x

[John Ralls]

We're almost ready to release 2.7.0, I just need to figure out why the build script locks up the Win10 VM build server.

I propose to create an "unstable" branch and release the 2.7.x series from that, so all 2.7.x bug fixes and any remaining work for the 2.8.x would go to that branch; long-term development could continue in master (e.g. Aaron Laws has started converting Account.c to Account.cpp).

Periodic merges would be maint->unstable and unstable->master with "periodic" meaning at least immediately before each 2.7.x release.

When we release 2.8.0, we'll also release 2.6.20, do a final merge maint->unstable, delete maint and rename unstable to maint. At that point we'll be back to two active branches until we start the 2.9 alpha releases around 4 years from now.

Any objections or concerns?

Regards,
John Ralls