Support for slack attachments

[Ashex]

Added support for passing in a proper list for slack attachments. This can be used in the following fashion:

from will.plugin import WillPlugin
from will.decorators import respond_to


class AttachmentsPlugin(WillPlugin):

    @respond_to("attachments")
    def attachments(self, message):
        attachments = [
            {
                "fallback": "Support ticket #1943",
                "pretext": "A new ticket has been filed",
                "title": "Ticket #1943: Can't reset my password",
                "text": "Help! I tried to reset my password but nothing happened!",
                "color": "#7CD197"
            }
        ]
        self.say("Here's your attachments", message=message, attachments=attachments)

[skoczen]

Wow, love this. Thanks much, @Ashex !

[skoczen]

This has been released in 2.1.3 - thanks again! :)