Add documentation for CI_PULL_REQUEST and update changelog
Simpler timers
Auto-disable mounted timers.
(put! control-ch ...) -> (raise! owner ...)
Merge pull request #3020 from circleci/pr-env

Populate CI_PULL_REQUEST with a URL for Coverall, etc. Fixes #2080
Merge commit 'c9cf0305f910594b27e0f24a0ca72439d2f3e07b'
Merge commit '900e0dc1fe66821b707a67e3c4f880b7d1583a88'