Top-level keys should not be options by default.

[acobster]

With the possible exception of a small set of well-known options like name, we should not default to interpreting top-level keys as option names and inserting them as options. Instead we should just require a top level options: key.

Consider the scenario where we want to define a common structure using YAML's merge syntax:

some_stuff: &some_stuff
  a:
  b:
  c:

combined_stuff:
  <<: *some_stuff
  d:
  e:
  f:

other_stuff:
  <<: *some_stuff
  custom: abcd

This will be interpreted as defining an option called some_stuff with the value of an array, which is probably not what we want. We should be able to do this instead:

some_stuff: &some_stuff
  a:
  b:
  c:

options:
  combined_stuff:
    <<: *some_stuff
    d:
    e:
    f:

  other_stuff:
    <<: *some_stuff
    custom: abcd

...which will only define combined_stuff and other_stuff as options.