Merge pull request #3 from jcushman/master

wsgiref compatibility fixes
request_uri: only generate REQUEST_URI manually if not provided by wsgi framework
only encode chars that are not allowed in path segment, per
http://tools.ietf.org/html/rfc3986#section-3.3
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* MatchPrefix is now superceded by MatchRegex, which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"
Fix #5, bringing back customParams optional params sent to cdx server
Rename archivalrouter.MatchRegex -> archivalrouter.Route, supporting regex/prefix matching
add redir_to_exact to turn off redirect to exact timestamp in RewritingReplayHandler
update README
Handle ArchivalUrl subclasses.