Add the exception's class as event group. use real hostname

* Use Socket.gethostname instead of stuff from the request env
    so the forwarded-for hostname isn't used.

* Use the reported exception's class as the event's group
    so events can be coalesced by service
Bump version to 0.2.0
Merge pull request #6 from crashlytics/host-and-group

Add the exception's class as event group. use real hostname