Exercise:
  The method validates_length_of checks the length of a
  model attribute. Add validation to the product model to check
  that the title is at least 10 characters long.
  
What I did:
  - I added the following line to the file product.rb in the app/models directory
  
      validates_length_of :title, :minimum => 10
      
    To find the syntax, I looked up the method on http://api.rubyonrails.com


Exercise:
  Change the error message associated with one of your
  validations.
  
What I did:
  - I changed the validation of the price, adding the :message option
  
      validates_numericality_of :price,
                                :message => "should be a number like 12.34"


Exercise:
  Add the product price to the output of the list action.

What I did:

  - I added a new column to the table in list.rhtml:
  
      <td>
        <span class="list-price"><%= h(product.price) %></span>
      </td>

  - I added a new entry in the depot.css stylesheet for list-price
