Tidy debug statements.
Support async-validate invocation.
0.0.2
Support readline configuration options.

So that a completer may be specified.
0.0.3
Support repeat option on validation error.
Improve cancel event handling.
Fix silent mode handling.

Such that a new readline interface is created whenever silent mode is
detected which breaks the history, a better solution is to pause and
resume the main readline interface and create a temporary one with the
mute stream.
0.0.4
Support trim option.
0.0.5
Implement default prompt formatting.
0.0.6
Support format string in item options.
Fix completer reference bug.

Also add stub transform method.
0.0.7
Change default format.
0.0.8
Improve default message handling.
0.0.9