Clarify if/when HEAD and OPTIONS should be supported
HEAD and OPTIONS methods are useful, particularly when using a web-based client, but also for low-bandwidth users who don't want to download lots of large certs unnecessarily during a refresh.
See https://github.com/hockeypuck/hockeypuck/issues/365, https://github.com/hockeypuck/hockeypuck/issues/368
Edited by Andrew Gallagher