screamer: dev branch

[Nikodemus Siivola]

I'm keeping "master" on Git the classic Screamer for now: no
intentional functional changes should occur there.

However, since I'm starting to discover things I want to change
around, I've added a "dev" branch where new developments can occur.

My plan is to make 3.21 an unofficial maintenance release: ANSI
cleanups and docs only, pretty much.

After 3.21 current "master" can become "classic" branch in deep
maintenance mode, and "dev" can be renamed "master".

Cheers,

-- Nikodemus