Rich "Attachment" Notifications Implemented

[m9]

I've finally implemented Attachment notifications, as suggested in #24

After a short discussion on IRC with @technicalpickles we've found probably a best way to implement this without extending core hubot functionality.

I've also wrote an example script that represents, how to use this feature. The code below will result with such message in a chat room:

# Description:
#   Demonstrating Slack Attachments.
#
# Commands:
#   hubot demo-attachment - Demo Attachement

module.exports = (robot) ->
  robot.respond /demo-attachment$/i, (msg) =>
    fields = []
    fields.push
      title: "Field 1: Title"
      value: "Field 1: Value"
      short: true

    fields.push
      title: "Field 2: Title"
      value: "Field 2: Value"
      short: true

    payload = 
      message: msg.message
      content:
        text: "Attachement Demo Text"
        fallback: "Fallback Text"
        pretext: "This is Pretext"
        color: "#FF0000"
        fields: fields

    robot.emit 'slack-attachment', payload

[evansolomon]

From a readability point of view, I think it makes sense to wait until the options are parsed and possible errors are logged to bind this listener.

[evansolomon]

Looks good to me. Since it's pretty slack-specific, would be good to get @grantmd's opinion.

[m9]

Thanks @evansolomon for your comments

[grantmd]

Thank you @balbeko for the code and @evansolomon for the reviews!

[technicalpickles]

I'd be curious to see is how you'd be able to write scripts that work for other adapters, while still being able to add slack-specific enhancements.

I'm also not sure if I'm 👍 on naming it custom. If you this is going to be slack-specific, may as well call it attach, because that's what they are called in the API documentation.

[m9]

@technicalpickles what's a best way to determine in script, what adapter is used?

[technicalpickles]

@balbeko some discussion about that in hubotio/hubot#647 , still need to put together a PR to make the name accessible though.