Kien

* FIX: `set echo` command now lists possible values for `STATE` variable.
* FEATURE: The command decorator now uses the decorated function as lookup object for
any unknown attributes that are referenced.
* FEATURE: `regex` validator now supports an optional message.

* FIX: Kien uses `functools.wraps` for decorators now.
* FEATURE: Improve command suggestions for partial command matches with too few arguments
* FEATURE: Transforms can request the transformation context with the `takes_transform_context`
decorator now. This is helpful for transforms that are dependent on the result of
transforms that ran before.

* FIX: The inject mechanism correctly handles default arguments now.
* FIX: If the last command didn’t carry a status code keep the one that was issued before.
* FEATURE: Take exact argument matches into account when displaying command suggestions.
* FEATURE: Add `on_result`, `on_dispatch` and `on_error` event hooks.

* FIX: Raise an exception if a dependency injection failed at runtime.

* BREAK: Signature of CommandResult changed, errors should now be handled
via `raise CommandError`.
* BREAK: `Console.send_error` is no longer part of the public API. Use `send_data`.
* FEATURE: Add json output-format support.
* FEATURE: Add `--failsafe-errors` option to runner that outputs errors
if `--failsafe` has been set.
* FEATURE: enable comments prefixed with the `` character. Comments carry the last
command status like they do in shells.

* FEATURE: Add `failsafe` decorator in utils module.
* FEATURE: Add `--failsafe` option to runner keeping the application from exiting.
* FEATURE: Output of a result is now terminated with two additional characters.
The first character is a space (`0x20`) or a bell (`0x07`) character depending
on the success of the command. The second is a null (`0x00`) character marking
the end of the result output.
* FEATURE: Add `--history` option for command history support.
* FEATURE: Various improvements for integrated help command.
* FEATURE: Subclassed Runner instances now have access to the console object.