Store answer values as custom data attribute
Convert text entry field into a proper form
Fill the input form with 1+1
Add a submit button to the form.

- Enables Casper submission
- form.submit apparently does not call
  onsubmit handlers
Add a white background for prettier screenshotting
Give more descriptive names to user input elements

- wrapping form = #command-line
- input box itself has name user-entry
Wrap results in output tags.
Handle_input needs refactoring