python-packages: prompt_toolkit 0.42 -> 0.43

New features:
- Added eventloop and patch_stdout parameters to get_input.
- Inputhook support added.
- Added ShowLeadingWhiteSpaceProcessor and ShowTrailingWhiteSpaceProcessor
  processors.
- Accept Filter as multiline parameter in 'shortcuts'.
- MultiColumnCompletionsMenu + display_completions_in_columns parameter
  in shortcuts.

Backwards incompatible changes (not used in nixpkgs):
- Layout.width was renamed to preferred_width and now receives a
  max_available_width parameter.