Intercept link clicks module

[wesleytodd]

https://github.com/wesleytodd/intercept-link-clicks

@nateps I figured I could knock this one out really quick. I pulled out what was in Nighthawk verbatim, then went through and added most of the stuff from here: https://github.com/derbyjs/tracks/blob/master/lib/History.js#L145

The only things I didn't add was your check for data-router-ignore and my check for the base path. I figured that our independent work can just add these kind of features after the main checks. I did that here in Nighthawk: https://github.com/wesleytodd/nighthawk/blob/intercept-clicks/lib/router.js#L135

What do you think? I tried to keep is simple, the main interface is the single function. I also moved over the unit tests from Nighthawk that covered that section. But it would probably need a bit more test coverage...