Fixed a couple of bugs related to the PM functionality

[rayman22201]

Hi! Your library is really awesome. It has been helpful in letting me creating a Slackbot very quickly.

I found a few bugs in the PM functionality and I thought I would pass my fixes along for your perusal.

getIM function:

• The self variable was never initialized. This caused the function to crash. (duh)
• The second search loop in the getIM function (lines 244 - 247) used the value of the getUser function without checking to make sure getUser didn't return null. If the term is not a user, the function would just crash before it even got to the third search loop that checks for channel ID.

  sendPM function:

• The sendPM originally would just crash if getIM returned null.
• I changed the behavior so that if getIM returns null (no private IM channel is found), the function will attempt to create a new private IM channel using reqAPI. It then adds that IM channel to the list of known IM channels, and sends the message to the newly created channel.

I tested this behavior on the bot that I have been working on that needs to send lots of PM's, and it seems to work like a charm :-)

[igorantun]

Awesome work @rayman22201! Thanks for contributing :)

[samhmills]

Agreed, 237 should be

var im = null, self = this;

The rest looks good though

[igorantun]

Great, thanks! :)