Fix Parser.parse docstring for 'location'
Refer to the `__location_map__` attribute, and expand the list of
supported locations to be complete (add `query` and `json_or_form`).
@@ -240,8 +240,9 @@ class Parser(object):
which accepts a request and returns a `marshmallow.Schema`.
:param req: The request object to parse.
:param str location: Where on the request to load values.
- Can be one of ``('json', 'querystring', 'form', 'headers', 'cookies',
- 'files')``.
+ Can be any of the values in :py:attr:`~__location_map__`. By
+ default, that means one of ``('json', 'query', 'querystring',
+ 'form', 'headers', 'cookies', 'files', 'json_or_form')``.
:param callable validate: Validation function or list of validation functions
that receives the dictionary of parsed arguments. Validator either returns a
boolean or raises a :exc:`ValidationError`.
