Apispec

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Features:

- Use ``raise from`` whenever possible (:pr:`763`).

Refactoring:

- Use a ``tuple`` rather than a ``namedtuple`` for "schema key" (:pr:`725`).

Other changes:

- Add type hints (:pr:`747`). Thanks :user:`kasium` for the PR.
- Test against Python 3.10 (:pr:`724`).
- Drop support for Python 3.6 (:pr:`727`).
- Switch to Github Actions for CI (:pr:`751`).

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

Bug fixes:

- Fix field ordering in "ordered" schema classes documentation (:issue:`714`).

Other changes:

- Don't build universal wheels. We don't support Python 2 anymore.
(:pr:`705`)
- Make the build reproducible (:pr:`669`).

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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.