Dice#roll stores the rolled value

* Instead of calling Side#value (which could change)
Rename Dice#rolled to Dice#result
Add alias methods to Dice#result
Rename Cup#rolled to Cup#result
Add alias methods to Cup#result
Add Cup#rolled_sides
Fix object type in documentation
Merge pull request #33 from rafaelgonzalez/fix-dice-rolled

Fix #rolled Dice and Cup methods