Bump version to 0.2.16
Tweak documentation; add script for running roverlay in b/g
Fixed bug in checklist "traffic light" reports when the target resource tested is not the RO itself.
Add local HTTP redirect cache for RO resources.

This is a weak attempt to reduce load on and mitigate errors from
redirection services like Purl.org.  What is really needed here is some
greater resilience in the face of certain kinds of HTTP failures.
HTTP_Session doRequest* methods return redirect URI as string; remove redundant code from ROSRS_Session
Add retry logic to roverlay service, and fix URI-redirect-cache bug introduced by earlier changes
Update revision history summaries
Merge branch 'develop' for version 0.2.16