Start explicit metadata argument for marshmallow

A side effect of re-locking dependencies is having a newer marshmallow.
This deprecates having `description=` as a keyword, and puts it in a
separate metadata arg instead.

This commit is the start of my search-and-replaceing to update to the new
format.

docs/source/extensions/actions.rst

@@ -18,7 +18,7 @@ Like properties, we use a special view class to identify a view as an action: ``
         Take an image capture and return it without saving
         """
         # Expect a "use_video_port" boolean, which defaults to True if none is given
-        args = {"use_video_port": fields.Boolean(missing=True)}
+        args = {"use_video_port": fields.Boolean(load_default=True)}
 
         # Our success response (200) returns an image (image/jpeg mimetype)
         responses = {

docs/source/extensions/example_extension/05_actions.py

@@ -91,7 +91,7 @@ class QuickCaptureAPI(ActionView):
     """
 
     # Expect a "use_video_port" boolean, which defaults to True if none is given
-    args = {"use_video_port": fields.Boolean(missing=True)}
+    args = {"use_video_port": fields.Boolean(load_default=True)}
 
     # Our success response (200) returns an image (image/jpeg mimetype)
     responses = {200: {"content": {"image/jpeg": {}}}}

docs/source/extensions/example_extension/06_tasks_locks.py

@@ -69,7 +69,7 @@ class TimelapseAPIView(ActionView):
             required=True, example=5, description="Number of images"
         ),
         "t_between": fields.Number(
-            missing=1, example=1, description="Time (seconds) between images"
+            load_default=1, example=1, description="Time (seconds) between images"
         ),
     }
 

docs/source/extensions/example_extension/07_ev_gui.py

@@ -102,7 +102,7 @@ class TimelapseAPIView(ActionView):
             required=True, example=5, description="Number of images"
         ),
         "t_between": fields.Number(
-            missing=1, example=1, description="Time (seconds) between images"
+            load_default=1, example=1, description="Time (seconds) between images"
         ),
     }
 

docs/source/extensions/marshaling.rst

@@ -23,7 +23,7 @@ A **field** describes the data type of a single parameter, as well as any other
 
 .. code-block:: python
 
-    fields.String(required=False, missing="Default value", example="Example value")
+    fields.String(required=False, load_default="Default value", example="Example value")
 
 A **schema** is a collection of keys and fields describing how an object should be serialized/deserialized. Schemas can be created in several ways, either by creating a ``Schema`` class, or by passing a dictionary of key-field pairs. Both methods will be discussed in the following examples.
 
@@ -43,7 +43,7 @@ For example, if you are creating an API route, in which you expect parameters ``
     class UserSchema(Schema):
         name = fields.String(required=True)
         age = fields.Integer(required=True)
-        job = fields.String(required=False, missing="Unknown")
+        job = fields.String(required=False, load_default="Unknown")
 
 To inform your POST method to expect these arguments, use the ``args`` class attribute:
 
@@ -63,7 +63,7 @@ Alternatively, if your schema is only used in a single location, it may be simpl
         args = {
             "name": fields.String(required=True),
             "age": fields.Integer(required=True),
-            "job": fields.String(required=False, missing="Unknown")
+            "job": fields.String(required=False, load_default="Unknown")
         }
 
         def post(self, args):
@@ -88,7 +88,7 @@ This JSON data is the parsed, converted into a Python dictionary, and passed as
         args = {
             "name": fields.String(required=True),
             "age": fields.Integer(required=True),
-            "job": fields.String(required=False, missing="Unknown")
+            "job": fields.String(required=False, load_default="Unknown")
         }
 
         def post(self, args):