Settings

added the `settings` api, plus implemented the setting for xpath compression.
added docs and tests

will squash once approved of course,

Oh, also had to add to wd.js to get the tests working. If we are ok with my implementation I'll push there. In the meantime you can clone [my fork of wd.js](https://github.com/jonahss/wd).

And then I'm going to go and update the rest of the clients....

(of course I'll squash, once we're through here ;)
It'd be nice if we could do all the xpathCompression checks in one place.  Preferably the server, since you're already doing it there.  Then you could eliminate these checks entirely and even guarantee that the xpathCompression key always exists and has the correct value even before it gets to bootstrap.