Envisage 7.0.0

This is a major release aimed at modernization and cleanup of some out-of-date
code. In particular, this release removes the IPython-related plugins, and
drops support for Python 3.6.

Thanks to:

• Mark Dickinson
• Chengyu Liu
• Corran Webster

Features

• There's a new unbind_extension_point function that reverses the effects
  of bind_extension_point. This can be useful for clean teardown. (#546)
• All id string constants that were previously available from envisage.ids
  are now also exported in envisage.api. Users are encouraged to import
  everything they need from envisage.api, and to open an issue if anything
  they need is not exported in envisage.api. (#508)

Changes

• When exiting a TasksApplication, the plugins are now stopped after
  exiting the event loop. Previously they were stopped while the event loop was
  still running, causing some lifecycle issues. (#524)
• The extension_registry argument to bind_extension_point is no
  longer optional, and ExtensionPointBinding will no longer look for
  an extension registry on the ExtensionPoint class. (#545)
• Operations that used to raise SystemError now raise something more
  appropriate. In particular, the PluginManager.start_plugin and
  PluginManager.stop_plugin methods now raise ValueError rather
  than SystemError when given an invalid plugin id. (#529)
• envisage.__version__ is no longer defined. If you need the Envisage
  version at runtime, use importlib.metadata to retrieve it. (#513)
• Python 3.6 is no longer supported. All current versions of Python (3.7
  through 3.11) are supported. (#513)

Fixes

• The repr of a Plugin instance now correctly uses the name of the
  plugin class. (#535)

Deprecations

• The EggPluginManager, EggBasketPluginManager and
  PackagePluginManager are deprecated, and will be removed in Envisage 8.0.
  (#540)
• The include and exclude traits on the PluginManager are
  deprecated, and will be removed in Envisage 8.0. (#544)

Removals

• Plugins and machinery related to IPython have been removed. Specifically,
  the IPythonKernelPlugin and IPythonKernelUIPlugin plugins have been
  removed, along with supporting classes InternalIPKernel and
  IPKernelApp. (#496)
• The ExtensionPoint.bind method has been removed. (#545)
• The previously deprecated safeweakref.ref class has been removed. (#522)
• Some legacy unmaintained examples have been removed. (#557)

Documentation

• The changelog is now included in the built documentation. (#550)

Tests

• Old-style namespace packages used for testing have been replaced with
  normal non-namespace packages. This fixes some warnings from the latest
  setuptools. (#543)
• The test suite now runs cleanly under pytest. (#539)
• Tests that are skipped due to a PySide6 problem should now be run
  if the version of PySide6 is recent enough. (#554)

Build

• Package configuration now uses pyproject.toml in place of the old
  setup.py-based configuration. (#513)
• Optional dependencies are no longer declared. (#513)
• A new style-checking workflow has been added that runs black, isort
  and flake8 over the codebase, and new code is expected to comply with
  black and isort configurations. (#549)
• A new documentation-build workflow has been added. The built documentation
  is uploaded as an artifact. (#551)