Produces general documentation for the interface

def documentation(self, add_to=None):
        """Produces general documentation for the interface"""
        doc = OrderedDict if add_to is None else add_to

        usage = self.interface.spec.__doc__
        if usage:
            doc['usage'] = usage
        if getattr(self, 'requires', None):
            doc['requires'] = [getattr(requirement, '__doc__', requirement.__name__) for requirement in self.requires]
        doc['outputs'] = OrderedDict()
        doc['outputs']['format'] = self.outputs.__doc__
        doc['outputs']['content_type'] = self.outputs.content_type
        parameters = [param for param in self.parameters if not param in ('request', 'response', 'self')
                                                        and not param in ('api_version', 'body')
                                                        and not param.startswith('hug_')
                                                        and not hasattr(param, 'directive')]
        if parameters:
            inputs = doc.setdefault('inputs', OrderedDict())
            types = self.interface.spec.__annotations__
            for argument in parameters:
                kind = types.get(argument, text)
                if getattr(kind, 'directive', None) is True:
                    continue

                input_definition = inputs.setdefault(argument, OrderedDict())
                input_definition['type'] = kind if isinstance(kind, str) else kind.__doc__
                default = self.defaults.get(argument, None)
                if default is not None:
                    input_definition['default'] = default

        return doc