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 ;)
Sleeps (static waits) are a bad test practice that we tell people to avoid but don't avoid ourselves in our own testsuite because we're lazy and elastic waits are a bit unapproachable with our current Promise-based API.

I think we should create a ticket as part of a CI effort/sprint and address it later