Dino Dex First Refactor

Let me know when you have a few minutes.  I want to go over a few of the questions you had which I haven't yet done anything with.
Sorry if I am repeating myself. My browser/github is acting funny today and it seems like my comments are disappearing!

There is no need for the assignment `@period = ...`. Just do:

```def period_type
  PERIOD_PERIOD_TYPES[@period]
end```