Customize readline

[wzy]

Describe the solution you'd like

Like readline, user can define its behavior by ~/.inputrc: prompt string, hotkeys, cursor shape.

Additional context

1. Press <C-L> to clear screen
2. Press .<TAB> to complete .q, .help, ...
3. Display man printf when user input printf( like the following figure display help(os.path.dirname) when user input os.path.dirname(.

[Axel Naumann]

I'd like us to switch to llvm::LineEditor - would that address that?