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
@ulissesalmeida it is a simple solution, but you are not defining structures of the domain, you are just split things that are pure data, so having files to represent just data might be confusing. And, since you are using Rails, due to some conventions, adding just `CONSTANTS` not classes to files, does not work because it is not following the convention.

The `.load` is :+1: