[tor-relays] What are the v1, v2, v3, v4 connections?

[William Denton]

"Since startup, we have initiated 0 v1 connections, 1 v2 connections, 0 v3 
connections, and 12345 v4 connections."

What are these different types of connections?  I can't find them in the docs, 
so I assume I'm not looking in the right place.  (And what does it mean that the 
1 v2 connection sneaked in?)

Bill
-- 
William Denton
Toronto, Canada
<https://www.miskatonic.org/>