More incompatible changes:

* command.handle() is now simply command()
* short help is '-?'. '-h' is used for --host too often.
* Server options '-d' and '-r' are no longer toggles for debugging/reloading.
  Instead, '-d' forces debugging on and '-D' forces it off,
  no matter what the default said.
* The command.prompt_* compatibility methods have beeen removed.
  (They were already heavily deprecated.)
A command with help=None will now get that help from the docstring

which is good for overriding.
Pass an initial non-None app to create_app