github refactor: Handle header_event explicitly.
github refactor: Handle header_event explicitly.

We get the header_event one level up the call
stack now, too.

It's somewhat annoying that we have our own
concept of "event" here, instead of just returning
our event handlers directly, or just calling them
directly, but it's a bit non-trivial to fix that
right away.

In passing, I remove the strange OR for "ping",
which is already a key in EVENT_FUNCTION_MAPPER.

showell/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,andersk/zulip,showell/zulip,andersk/zulip,zulip/zulip,andersk/zulip,rht/zulip,showell/zulip,showell/zulip,eeshangarg/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,showell/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,kou/zulip,punchagan/zulip,kou/zulip,rht/zulip,rht/zulip,punchagan/zulip,punchagan/zulip,showell/zulip,zulip/zulip,zulip/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,punchagan/zulip,andersk/zulip,showell/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,eeshangarg/zulip,rht/zulip,hackerkid/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,hackerkid/zulip,eeshangarg/zulip