Apptools 5.0.0

This is a major release mainly relating to code modernization. In this release,
support for Python versions < 3.6 have been dropped. Numerous dated
sub-packages and code fragments have been removed. Additionally, there were
various fixes and documentation updates.

Fixes

• Fix SyntaxWarning in persistence.file_path (#116)
• Fix container items change event being saved in preferences (#196)
• Fix synchronizing preference trait with name *_items (#226)

Deprecations

• Deprecate apptools.undo subpackage (undo was moved to pyface) (#250)

Removals

• Remove appscripting subpackage (#172)
• Remove template subpackage (#173)
• Remove permission subpackage (#175)
• Remove lru_cache subpackage (#184)
• Remove support for Python 2.7 and 3.5 (#190)
• Remove the apptools.sweet_pickle subpackage. Note that users of
  sweet_pickle can in some cases transition to using apptools.persistence
  and pickle from the python standard library (see changes made in this PR to
  apptools.naming for more info) (#199)
• Remove help subpackage (#215)
• Remove NullHandler from apptools.logger (#216)
• Remove apptools.logger.filtering_handler and apptools.logger.util submodules (#217)
• Remove deprecated create_log_file_handler function (#218)
• Remove use of apptools.type_manager from apptools.naming. Then,
  remove apptools.type_manager entirely. Finally, remove
  apptools.naming.adapter. (#219)
• Remove apptools.persistence.spickle submodule (#220)
• Remove apptools.naming.ui sub package (#233)

Documentation changes

• Update documentation for Preferences (#198)
• Add a brief section to documentation for apptools.naming (#221)
• Document the apptools.io and apptools.io.h5 sub packages (#237)
• Fix a few broken links in the documentation (#248)

Test suite

• Fix AttributeError on Python 3.9 due to usage of base64.decodestring in tests (#210)
• Make optional dependencies optional for tests (#260)

Build System

• Add extras_require to setup.py for optional dependencies (#257)