Bidirectional - close #12

[Jaykul]

It's a lot of changes (starting with changing to using the slack-client), and I'm sure the whole thing could be done better (I'm not a node guy), but it's working nicely for us, so I figured you'd like to have the code.

Importantly, I stripped the "op" feature because our bot isn't opped and it kept causing an error to be printed, and I also stripped the silent option (what is a silent bridge?) and added some features around formatting and message length.

We still have some issues ;-)

[jimmyhillis]

Thanks so much for this @Jaykul - i've been completely slammed this week so I'll get into this and see if we can make it ready for a merge as soon as I can in the next day or so.

[derfsubterfuge]

What is the status of this?