[anti-censorship-team] Tor Browser with Turbo Tunnel–enabled Snowflake

[David Fifield]

Cecylia reminded me that building the quic-go version is trickier
because quic-go has an unstable API, and the version of quic-go
currently being used in the Tor Browser build is API-incompatible with
what you'll get if you just "go get" or "go build". The snowflake repo
doesn't yet have a go.mod file to lock in specific versions.

So the build instructions are a little bit more involved:
	git clone https://git.torproject.org/pluggable-transports/snowflake.git
	cd snowflake
	git remote add dcf https://git.torproject.org/user/dcf/snowflake.git
	git fetch dcf
	git checkout 5eff0f3ba406eb7d8cd90711edab7de7d7bda4fa
	for d in broker proxy-go server; do (cd $d && go get); done
	(cd $GOPATH/src/github.com/lucas-clemente/quic-go && git checkout 907071221cf97f75398d9cf8b1174e94f56e8f96)
	(cd $GOPATH/src/github.com/marten-seemann/qtls && git checkout 65ca381cd298d7e0aef0de8ba523a870ec5a96fe)
	for d in broker proxy-go server; do (cd $d && go build); done

Alternatively, you can change IdleTimeout to MaxIdleTimeout in the
quic.Config structures; I think that's the only API change.