3.0 - Add an intro chapter for the ORM and start validation chapter.

I've added the introduction chapter for the ORM, and started the docs for the validation package. I was thinking of **not** including detailed method docs for the Validation class, and instead link to the API docs, as currently the book docs just duplicate the API docs making maintenance more difficult.

I was thinking of making the Validation docs more of a how-to/guide and less of an API reference. I plan on adding more thorough examples to the API docs as a replacement for the book content that will be removed.