Update jolt book to reflect API changes

[marsella]

In #616, the code generated by the Jolt binary changed. However, that PR didn't update the Jolt book to reflect those changes.

• Fix the "Project Tour" section of the quickstart page to have the correct generated code.
• Fix the hosts page to have the correct generated code, and update the description.
• Review the rest of the book to see if there are other places with outdated APIs.