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New features:
- Added `prompt_toolkit.layout.utils.iter_token_lines`.
- Allow `None` values on the focus stack.
- Buffers can be readonly. Added `IsReadOnly` filter.
- `eager` behavior for key bindings. When a key binding is eager it will be
executed as soon as it's matched, even when there is another binding that
starts with this key sequence.
- Custom margins for BufferControl.
Fixes:
- Don't trigger autocompletion on paste.
- Added `pre_run` parameter to CommandLineInterface.
- Correct invalidation of BeforeInput and AfterInput.
- Correctly handle transparency. (For floats.)
- Small change in the algorithm to determine Window dimensions: keep in the
bounds of the Window dimensions.
Backwards-incompatible changes:
- There a now a `Lexer` abstract base class. Every lexer should be an instance
of that class, and Pygments lexers should be wrapped in a `PygmentsLexer`
class. `prompt_toolkit.shortcuts` still accepts Pygments lexers directly for
backwards-compatibility.
- BufferControl no longer has a `show_line_numbers` argument. Pass a
`NumberedMargin` instance instead.
- The `History` class became an abstract base class and only defines an
interface. The default history class is now called `InMemoryHistory`.