Add character class selection

This PR is related to issue #8. 

To complete this feature we still need to do:

- [x] Character class selection screen
- [x] Display the class description
i don't have enough experience to ensure if it is better or not, but since this method deal with arrays, I think that the equipments should be an array also and not deal with safe stuff.

I think that the caller should deal with this, either wrapping in array or using `possible_nil || []`, let the check to the higher level of use instead moving the problem to the bottom level of the code. It is desirable that your core logic works, without dealing with this blank values.