Summoner with meta

This is the same as https://github.com/petems/riot_api/pull/13 except instead of having to call

`RiotApi::Model::<model_name>.new ...`

in all the Resource classes, you can just call

`build_model ...`

and the `base` class handles the rest.

See the changes to `lib/riot_api/resource/base.rb` for the big difference.  Or just compare #13 to this.

Again, no tests yet.