Adding Google Analytics to doc pages.

[mikeal]

This adds the same analytics line to our documentation as we have on the rest of the website.

[evanlucas]

do we care that this will be executed when run locally?

[jasnell]

hmm.. fwiw, I care that this would be executed when run locally. Couldn't this be injected only when the docs are on the website. -1 on this being here.

[mikeal]

Good point, pinging @nodejs/build to see if we can get this worked into that process.

[jbergstroem]

SSI?

Edit: would work like so:

<!--# include file="tracking.html" -->

[jasnell]

Given the -1's can we close this and defer the discussion over to the nodejs/nodejs.org repo?

[jbergstroem]

@jasnell doesn't seem to be an open issue there. Want to create one?

[jbergstroem]

We could use the sub module as well, but I'd like to do some performance measuring first seeing how we push 500mbit/sec+.

[jasnell]

Done: nodejs/nodejs.org#709

[jbergstroem]

Lets close it and continue over there then.