Add a "close" method to the API

[EricForgy]

Note that since

close(w) = @dot w close

depends on @ dot, I moved api.jl to AtomShell so @ dot is defined first.

Closes #28

[pfitzseb]

Wouldn't it make more sense to define close(w::Window) here, since all the other window managing methods are there as well?

It's a much smaller change then and the restructuring wouldn't be needed.

[EricForgy]

That does make more sense. Thanks. I'll fix it.

[EricForgy]

Maybe a rebase would be cleaner? (Still learning. Sorry.)

[pfitzseb]

Hm, probably. Especially since close is defined twice now. :) You could also locally revert your commits, create a new one and force push that to this branch.
Also, I think you need to explicitly import it from Base in window.jl, since Base.close exists.

[EricForgy]

I suck :D

Almost there :)

[EricForgy]

So simple, huh? :) Thanks for your patience.

[pfitzseb]

Also export it and I'll merge ;)

Edit: Oh wait, is that even necessary?! It isn't, right? If so, nevermind.