Apispec

******************

Features:

- Add ``lazy`` option to component registration methods. This allows to add
components to the spec only if they are actually referenced. (:pr:`702`)
- Add ``BasePlugin.header_helper`` and ``MarshmallowPlugin.header_helper``
(:pr:`703`).

Bug fixes:

- Ensure plugin helpers get component copies. Avoids issues if a plugin helper
mutates its inputs. (:pr:`704`)

******************

Features:

- Rename ``doc_default`` to ``default``. Since schema metadata is namespaced in
a single ``metadata`` parameter, there is no name collision with ``default``
parameter anymore (:issue:`687`).
- Don't build schema component reference in
``OpenAPIConverter.resolve_nested_schema``. This is done later in
``Components`` (:pr:`700`).
- ``MarshmallowPlugin``: resolve schemas in ``allOf``, ``oneOf``, ``anyOf`` and
``not`` (:pr:`701`). Thanks :user:`stefanv` for the initial work on this.

Other changes:

- Refactor ``Components`` methods to make them consistent. Use ``component_id``
rather than ``name``, remove ``**kwargs`` when unused. (:pr:`696`)

********************

Features:

- Resolve all component references in paths and components. All references must
be passed as strings, not as a ``{$ref: '...'}}`` dict (:pr:`671`).

Other changes:

- Don't use deprecated ``missing`` marshmallow field attribute but use
``load_default`` instead (:pr:`692`).
- Refactor references resolution. ``get_ref`` method is moved from ``APISpec``
to ``Components`` (:pr:`655`). ``APISpec.clean_parameters`` and
``APISpec.clean_parameters`` are now private methods (:pr:`695`).
- Drop support for marshmallow < 3.13.0 (:pr:`692`).

******************

Bug fixes:

- Correct spelling of ``'null'``: remove extra quotes (:issue:`689`).
Thanks :user:`mjpieters` for the PR.

******************

Features:

- Document ``deprecated`` property from field metadata (:pr:`686`).
Thanks :user:`greyli` for the PR.
- Document ``writeOnly`` and ``nullable`` properties from field metadata
(:pr:`684`). Thanks :user:`greyli` for the PR.

******************

Features:

- Support ``Pluck`` field (:pr:`677`). Thanks :user:`mjpieters` for the PR.
- Support ``TimeDelta`` field (:pr:`678`).