Should resolve #4 -- supports pywb running as a non-root app
* Instead of relying on REQUEST_URI, pywb constructs a
REL_REQUEST_URI, from PATH_INFO + QUERY_STRING.
SCRIPT_NAME auto-added to prefix
* MatchPrefix is now superceded by MatchRegex, which
can match a plain string -- collId defaults to the full match
* Added optional archivalurl_class to router to allow for customized
ArchivalUrl implementations to be specified
* run.sh can test on a non-root mountpoint, eg. ./run.sh "/approot"