Documenting path parameters

How can I document path parameters? I expected the following to work:

````python
from apispec import APISpec
from apispec.ext.marshmallow import MarshmallowPlugin
from flask import Flask, Blueprint
from flask_apispec import FlaskApiSpec, MethodResource, doc

app = Flask(__name__)
api_blueprint = Blueprint('api', __name__, url_prefix='/api/')

app.config.update({
'APISPEC_SPEC': APISpec(
'Pets pets pets',
'0.0.1',
'2.0',
[MarshmallowPlugin()]
)
})

class PetResource(MethodResource):
@doc(
parameters=[
{
'name': 'pet_id',
'in': 'path',
'description': 'The ID of the pet',
'required': True,
'type': 'string',
'example': '0c3ca635-2d58-4548-ad59-027fe4983e2c'
}
]
)
def get(self, **kwargs):
return None

pet_view = PetResource.as_view(PetResource.__name__)
api_blueprint.add_url_rule('/pet/', view_func=pet_view)

app.register_blueprint(api_blueprint)

docs = FlaskApiSpec(app)
docs.register(PetResource, endpoint=PetResource.__name__, blueprint=api_blueprint.name)

app.run(debug=True)
````

but this produces the following swagger:
````json
{
"definitions": {},
"info": {
"title": "Pets pets pets",
"version": "0.0.1"
},
"parameters": {},
"paths": {
"/api/pet/{pet_id}": {
"get": {
"parameters": [
{
"in": "path",
"name": "pet_id",
"required": true,
"type": "string"
}
],
"responses": {}
}
}
},
"responses": {},
"securityDefinitions": {},
"swagger": "2.0",
"tags": []
}
````
As seen I would like to be able to provide a description and an example value.

Start at the @doc parameters passed to PetResource.get and the FlaskApiSpec registration that produces /api/pet/{pet_id}; compare the generated Swagger parameter object with the supplied description and example. Done means the generated path parameter retains both fields.

Written by the indexing model from the issue text.