Sets boolean to prevent user intervention. This is the same as setting Vedeu::Config::API#interactive to false.

# Same as `standalone true` or `interactive false`.
Vedeu.configure do
  standalone!
  # ...
end

# => Disallow user input.
Vedeu.configure do
  standalone true
  # ...
end

# => Allow user input.
Vedeu.configure do
  standalone false
  # ...
end