Prompt-toolkit

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Bug fixes:
- Don't use the predefined ANSI colors for colors that are defined as RGB.
(Terminals can assign different color schemes for ansi colors, and we don't
want use any of those for colors that are defined like aabbcc for instance.)
- Fix in handling of CPRs when patch_stdout is used.

Backwards incompatible changes:
- Change to the `Buffer` class. Reset the buffer unless the `accept_handler`
returns `True` (which means: "keep_text"). This doesn't affect applications
that use `PromptSession`.

New features:
- Added `AdjustBrightnessStyleTransformation`. This is a simple style
transformation that improves the rendering on terminals with light or dark
background.
- Improved performance (string width caching and line height calculation).
- Improved `TextArea`:
* Exposed `focus_on_click`.
* Added attributes: `auto_suggest`, `complete_while_typing`, `history`,
`get_line_prefix`, `input_processors`.
* Made attributes writable: `lexer`, `completer`, `complete_while_typing`,
`accept_handler`, `read_only`, `wrap_lines`.

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New features:
- Added dictionary completer (off by default).
- Added fuzzy completion (off by default).
- Highlight keywords in completion dropdown menu.
- Enable universal wheels.

Fixes:
- Fixed embedding repl as asyncio coroutine.
- Fixed patching stdout in embedded repl.
- Fixed ResourceWarning in setup.py.

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- Fixed ptipython.
- Fixed config: setting of color depth.
- Fixed auto-suggest key bindings.
- Fixed Control-D key binding for exiting REPL when (confirm_exit=False).
- Correctly focus/unfocus sidebar.
- Fixed open_in_editor and suspend key bindings.

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- Allow changing the min/max brightness.
- Some changes for compatibility with the latest prompt_toolkit.

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Fixes:
- Don't crash the history browser when there was no history.
- Set last exception in the sys module, when an exception was raised.
- Require prompt_toolkit 2.0.5.

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Upgrade to prompt_toolkit 2.0.x.