change PerlHandler -> PerlResponseHandler in docs

According to
http://perl.apache.org/docs/2.0/user/handlers/http.html#HTTP_Request_Cycle_Phases
"the PerlHandler directive has been renamed to PerlResponseHandler to
better match the corresponding Apache phase name (response)."
Reflect changes and update list of contributors.
Remove duplicate POD in lib/Dancer2.pm.

There were two copies one below the other.
Provide a better reference for the mailing list.

URL, with some clarifications. It's hard to know how to subscribe from
the E-mail address alone.