Discourage checking hash fields in `object`.

It's glassbox testing to say that an object must contain certain hash fields and should not be encouraged. Unfortunately the object doc example spends half its time on this.

This is particularly egregious with end. This requires that the object contain exactly certain specific fields and no others. And end only applies to certain parts of the object description complicating how the user expects end to work.

To that end...

• Remove field and end from the object docs.
  • Leave them working for backwards compat.
• Allow hash, array, and bag to work inside object.

This eliminates a bunch of redundancy in object with hash and array, and it allows the object docs to focus on blackbox testing.

Start by locating the object documentation, its implementation, and the tests covering field, end, hash, array, and bag. Verify the requested documentation removals, backward compatibility, and nested behavior; done means the tests pass and the object docs no longer encourage glassbox field checks.