Added `clize.parser.use_class`, a parameter converter function factory that takes up to one parameter class for each python parameter type.
`default_converter` is now made using `use_class`.
The parameter conversion logic moved from `Parameter` to `CliSignature`.
Using `**kwargs` in a signature to be converted will, for now, raise an error.
Allow parameters to specify extra parameter instances to be added along themselves. Added Parameter.IGNORE as a parameter flag, also available for parameter converters to return.
Added clize.extra.mapped and one_of
Added kwargs-forwarding to clize.parser.use_class
Added clize.parser.use_mixin