Code autoformatting

The IPython terminal can now auto format your code just before entering a new line or executing a command. To do so use the --TerminalInteractiveShell.autoformatter option and set it to 'black'; if black is installed IPython will use black to format your code when possible.

IPython cannot always properly format your code; in particular it will auto formatting with black will only work if:

• Your code does not contains magics or special python syntax.
• There is no code after your cursor.

The Black API is also still in motion; so this may not work with all versions of black.

It should be possible to register custom reformatter, though the API is till in flux.