Create Version 2 of the Humbug Hook Payload, Rename Humbug->Zulip

This adds additional fields to help users customize where their github
traffic ends up, and helps filter the traffic for particularly noisy
repositories.

This also rebrands the Humbug hook as Zulip, to reflect the change
in Company name.
Revise Zulip documentation
Fixup Humbug/Zulip unit test
Merge pull request #783 from acrefoot/acrefoot

Change title of Humbug Integration to Zulip to reflect company name change. Also update configuration spec.