Add the load of the races respository files.

The main idea here is add some convention to add new content data for races, items, character classes, backgrounds and etc.

I used a little bit of meta programming. XD
I liked the idea of the yaml. I think it will be more clear for sure. I thought load the ruby files will be simpler haha.

We can move these yamls to `db/seeds/`. Inside of `seeds` directory we'll have `seeds/backgrounds/*`, `seeds/races/*` And have a model to load these files given an key, for example:  `Repository.load(:backgrounds); Repository.load(:races);`.

What do you think about this idea and `api` ?