User Story 13, Add a Review for a Book

[iandouglas]

As a Visitor,
When I visit a book's show page
I see a link to add a new review for this book.
When I click on this link, I am taken to a new review path.
On this new page, I see a form where I can enter:
- a review title
- a username as a string
- a numeric rating that can only be a number from 1 to 5
- some text for the review itself
When the form is submitted, I should return to that book's
show page and I should see my review text.

Users are created if they do not already exist.
User names should be converted to Title Case before saving.
User names should be unique within the system.
If user existed in the database, this review is associated
with that user.

Checklist:

• base code tests are written
• base code is written to pass tests
• edge case ("sad path") tests written
• edge case code written
• code is reviewed
• branch is merged
• all tests still pass

child of #18

child of #33