Pyface 7.3.0

The most significant change introduced in this minor release is the
replacement of Traits on_trait_change-based listeners with the new Traits
observation framework.

This release is only compatible with Traits >= 6.2.0 i.e. the most recent
version of Traits.

Highlights of this release

• Replace use of Traits on_trait_change with observe.

Detailed changes

Thanks to:

• Aaron Ayres
• Kit Yan Choi
• Rahul Poruri
• Corran Webster

Fixes

• Fix undo/redo merge bugs. (#885)
• Fix importing QtWebEngine after toolkit selection. (#853)

Documentation

• Improve api documentation for pyface.tasks submodules. (#844)
• Improve api documentation for pyface.undo and
  pyface.undo.action submodules. (#847)
• Improve api documentation for pyface.action and
  pyface.tasks.action submodules. (#843)
• Use viewcode sphinx extension. (#851)
• Address a few sphinx warnings. (#846)

Build, Tests and Continuous Integration

• Stop running CI on traits 6.0. (#865)
• Skip test if wx is not installed. (#867)
• Declare python_requires to support Python >= 3.6. (#850)

Maintenance and code reorganization

• Replace use of traits on_trait_change with observe. (#892, #882,
  #881, #880, #870, #864)
• Import from traits.api where possible. (#866)
• Expose keyboard focus on Widgets. (#862)
• Remove support for PySide. (#861)
• Remove Python 2 sip configuration for Qt toolkit backends. (#860)
• Remove coverage reporting on PRs. (#855)
• Update year range in copyright headers. (#854)