Add static data endpoints (#12)

I think we answered most of my questions in the other thread, but I wanted to throw two more out there:

1. The 'realm' endpoint was different enough and seemingly useless enough that I decided to omit it for now. I can implement that if needed.
2. Right now, I'm returning `OpenStruct`s instead of `Lol::Model`s for the static endpoints. The static endpoints seem to return slightly different objects than their non-static counterparts, so I can't reuse the existing `Lol::Model`s for `Champion`, `Rune`, etc. I can create `Lol::Static::Model`s or something for each of them, but the `OpenStruct` solution seems fairly flexible. I think the big reason to implement concrete classes for each would be if more behavior were added, but maybe I'm overlooking something. Happy to do this work if needed.

Let me know if you want anything cleaned up before merging!