Release 7.0.0

TraitsUI 7.0.0 is a major release which focuses on modernization of the
codebase. This release includes updating the WxPython backend to support
WxPython 4, an effort led by Rob McMullen's first cut at support, with
help from a number of other people, particularly Per Brodtkorb. It also
updates the code to use new features of Traits 6, and just like Traits 6,
this release drops support for Python 2.

In addition to the modernization, this code fixes many bugs and adds some
useful new features, including:

• a DatetimeEditor to go with the new Datetime trait in Traits 6
• an API to add placeholder text to a TextEditor
• support for the LEDEditor in Qt

Finally, the documentation has been improved, adding sections about some
of the internals of the TraitsUI mechanisms. Additionally, the Examples,
Demos and Tutorials have been improved and cleaned-up, including fixing and
unifying the demo viewer codebase.

Thanks to Per Brodtkorb, Christian Brodbeck, Kit Choi, Mark Dickinson, Matt
Hancock, Sandhya Govindaraju, Midhun Madhusoodanan, Rob McMullen, Shoeb
Mohammed, Eric Olsen, Roberto Preste, reckoner, Jonathan Rocher, Scott
Talbert, Corran Webster.

Enhancements

• Documentation improvements (#720, #724, #723, #778)
• WxPython 4 compatibility and support (#708, #736, #762, #772, #775, #776)
• Traits 6 compatibility and enhancements (#689, #690, #693, #695, #713, #727, #770)
• Style improvements (#648, #771)
• Add placeholder text option for TextEditor (#735)
• Examples clean-up and unification (#697, #702, #703, #705, #711, #712, #777)
• Add a DatetimeEditor (#719, #730)
• Refactor and clean-up of base Editor class (#685, #686, #688)
• Remove use of Category classes from TraitsUI (#654)
• Add LEDEditor for Qt (#635)
• Add 'docs' command to etstool.py (#624)
• Add TabularAdapter to traitsui.api (#627)
• Enhancements to CI and testing (#683, #714, #740)

Fixes

• Documentation fixes (#546, #766)
• Fix cgi.escape for Python 3.8 (#780)
• Log exceptions in table sorting (#751)
• Use TupleEditor for traits derived from BaseTuple (#747)
• Fixes for Undo/Redo (#733)
• Add explicit redraw for TableEditor selection (#721)
• Fixes for Qt5 support (#709)
• Fix bugs in color functions (#707, #744)
• Fix importing of ProgressColumn and EditColumn (#691)
• Set initial focus item correctly in Qt (#602)
• Fix text elision test on some platforms (#644)
• Fix a bug with TableEditor column clicking (#669)
• Fix typo in progress column exception (#662)