Prompt-toolkit

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Fixes:
- Again, fixed the race condition in `ThreadedHistory`. Previous fix was not
correct.

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Fixes:
- Fixed a race condition in `ThreadedHistory` that happens when continuously
pasting input text (which would continuously repopulate the history).
- Move cursor key mode resetting (for vt100 terminals) to the renderer. (Mostly
cleanup).

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New features:
- Poll terminal size: better handle resize events when the application runs in
a thread other than the main thread (where handling SIGWINCH doesn't work) or
in the Windows console.

Fixes:
- Fix bug in system toolbar. The execution of system commands was broken.
- A refactoring of patch_stdout that includes several fixes.
* We know look at the `AppSession` in order to see which application is
running, rather then looking at the event loop which is installed when
`StdoutProxy` is created. This way, `patch_stdout` will work when
prompt_toolkit applications with a different event loop run.
* Fix printing when no application/event loop is running.
* Fixed the `raw` argument of `PatchStdout`.
- A refactoring of the `ThreadedHistory`, which includes several fixes, in
particular a race condition (see issue 1158) that happened when editing
input while a big history was still being loaded in the background.

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New features:
- Improved `WordCompleter`: accept `display_dict`. Also accept formatted text
for both `display_dict` and `meta_dict`.
- Allow customization of button arrows.

Fixes:
- Correctly recognize backtab on Windows.
- Show original display text in fuzzy completer if no filtering was done.

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New features:
- Handle c-tab for TERM=linux.

Fixes:
- Improve rendering speed of `print_formatted_text`. (Don't render styling
attributes to output between fragments that have identical styling.)
- Gracefully handle `FileHistory` decoding errors.
- Prevent asyncio deprecation warnings.

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New features:
- Added `validator` parameter to `input_dialog`.

Fixes:
- Cope with stdout not having a working `fileno`.
- Handle situation when /dev/null is piped into stdin, or when stdin is closed
somehow.
- Fix for telnet/ssh server: `isatty` method was not implemented.
- Display correct error when a tuple is passed into `to_formatted_text`.
- Pass along WORD parameter in `Document._is_word_before_cursor_complete`.
Fixes some key bindings.
- Expose `ProgressBarCounter` in shortcuts module.