Migrate from using readline to prompt-toolkit

[tleonhardt]

This PR migrates from using GNU Readline for user input, tab-completion, and history to using prompt-toolkit for the same purpose.

prompt-toolkit is a pure-Python readline replacement that is fully cross-platform compatible and doesn't rely on the presence of underlying C dynamic libraries. It also opens the door to some advanced features in the future.

All use of readline is removed and the cmd2.rl_utils module has been deleted. There is a new cmd2.pt_utils module in its place. Currently all linting is passing and the documentation builds. This is essentially final draft that needs more testing. There are likely a some things that need to be considered related to asynicio support, signal handlers, and blocking popen calls.

All tests are passing on all platforms. I have done some manual testing on both macOS and Linux. But I don't have a Windows VM to do any manual testing on Windows however.

NOTE FOR REVIEWERS: The substantive code changes are in the 3 following files (all in the cmd2 directory):

• argparse_completer.py (modified)
• cmd2.py (modified)
• pt_utils.py (new)

TODO:

• Fix so tab-completion hints shown up above or below the prompt but not in the the bottom bar
• Fix tab completion for for command/sub-command names and arguments so it uses prompt-toolkit completion
• Fix subcommand suggestion for alias create <TAB> - currently showing nothing
• Increaes code coverage for new code
• Modify getting_started.py example to show how to use the optional bottom toolbar feature
• Update documentation
• Self review and code / comment cleeanup
• Check type-hints for new/modified methods and functions
• Verify that all arguments to cmd2.Cmd.read_input work like they did previously - test using examples/read_input.py
• Do a bunch of manual testing related to edge cases on all platforms
  • Windows
  • macOS
  • Linux
• Think about interactions with signal handlers
  • Ensure <Ctrl>+c works for SIGINT when using shell command - need to fix how prompt is redrawn after
  • Ensure terminated processes still properly handle SIGHUP/SIGTERM so that cmd2 exit handler runs to save persistent history and such
  • Should we worry about SIGKILL? - used to work fine and works normally now, but not anymore if inside ppaged (get traceback with termios.error)
• Thank about blocking calls to things like popen
  • Ensure output redirection works, to both file and clipboard
  • Ensure piping command output to shell command works
  • Ensure ppaged works properly like it did before - works, but doesn't handle SIGKILL correctly - get traceback
• Provide a flag to use readline-style completions instead of the prompt-toolkit style
• Dynamically switch from CompleteStyle.COLUMN to CompleteStyle.MULTI_COLUMN when there are a lot of completions - based on a settable which defaults to 7; switching disabled when user specifies READLINE_LIKE style
• Test in embedded py and ipy shells
  • Make sure locals self still works correctly in ipy
  • Make sure locals self still work correctly in py
  • See if we can get tab-completion working in embedded Python py shell for systems with LibEdit
• Think about whether there might be a race condition risk with self._in_prompt - I added a threadling.lock object to protect access to self._in_prompt to be safe
• Make sure we are happy with test coverage for new code
• Think about asyncio cases - prompt-toolkit natively uses asycnio and starts an event loop
  • Fix examples/async_call.py example to account for prompt-toolkit starting an asyncio event loop
  • Investigate whether cmd2 can use asyncio to replace things like self.terminal_lock, async_alert, and async_update_prompt - removed self.terminal_lock and updated sync_alert, and other stuff as well as async_printing.py example; also removed unused async_refresh_prompt and need_prompt_refresh methods
  • Can we remove the requirement for cmd2 apps to run in the main thread? - I don't think so. From what I can see, prompt-toolkit needs to run in the main thread for various reasons, though it does have good support for handling backkground tasks in other threads
  • Review example for how include async do_* commands is in examples/async_commands.py - if we are happy with it, we can move the decorator there into cmd2/decorators.py and the utility function into cmd2.utils.pyand add some unit tests
• Make sure changes are well documented in both CHANGELOG.md and in the Zensical documentation

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.17%. Comparing base (cb0c75e) to head (d6117d5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1553      +/-   ##
==========================================
+ Coverage   98.94%   99.17%   +0.22%     
==========================================
  Files          21       21              
  Lines        4942     4940       -2     
==========================================
+ Hits         4890     4899       +9     
+ Misses         52       41      -11     

Flag	Coverage Δ
unittests	99.17% <100.00%> (+0.22%)	⬆️

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