Some of the changes do not appear to have a potential race condition,
so there it is purely a refactor,
while in others (e.g. in broker.go and in proxy/lib/snowflake.go)
we do use the same variable from multiple threads / functions.
This package contains a CacheURL function that modifies a URL to be
accessed through an AMP cache, and the "AMP armor" data encoding scheme
for encoding data into the AMP subset of HTML.