Added urlview keybinding

1.  A shortcut of 'b' was used as the default binding for passing
comment body text to urlview (this is similar to the default of C-b in
the 'mutt' text email client)
2.  The `comment_urlview` SubmissionController function was added to
recieve the SUBMISSION_OPEN_IN_URLVIEWER keypress request.
3.  The `open_urlview` terminal function was added to handle the urlview
request.  It passes the comment body data to urlview via a Popen
process.
4.  A test case was added to ensure this new code path is executed
5.  Small formatting changes, mostly line length

scripts/rtv.1.template

@@ -28,6 +28,10 @@ for future sessions. You can disable this behavior by setting the option
 Text editor to use when editing comments and submissions. Will fallback to
 \fI$EDITOR\fR. 
 .TP
+.BR RTV_URLVIEWER
+Url Viewer to use to extract links from comments.  Requires a compatible 
+Url Viewer to be installed
+.TP
 .BR BROWSER
 Web browser to use when opening links.
 .TP