This adds threading support officially.

[gbin]

It is only implemented on Slack at the moment.

• adds a parent field to Message signaling to backends that it is a threaded
  response.
• retrofit in_reply_to as a signal to thread by putting this message as
  parent without changing the frm/to behavior.
• adds an optional threaded boolean for the build_reply & co that needs
  to be implemented by the backends (similar category as private).

[sijis]

I'll look at this more closely over the weekend. I'm not 100% familiar with the threading model, however, if you can show a couple of example usages that would be great!

[gbin]

@sijis It allows you to start message threads like this instead of a standard response:

It did this just by supplying the old in_reply_to parameter here:
https://github.com/gbin/err-standup/blob/master/standup.py#L176

You can retrofit this feature to existing commands also by tweaking the config and add to config.py:

DIVERT_TO_THREAD = ('help',)

This is similar to DIVERT_TO_PRIVATE but for THREADS.

I'll do a pass on documenting all that on another PR once we agree on the API.

[sijis]

Ahhh! I was thinking python threads.
I like that this feature being added. Again I'll try and poke at this and provide any feedback.

[gbin]

I timeouted on this, merged it.