Support `CTRL`+`W`/`CTRL`+`BACKSPACE`/`CTRL`+`DELETE` in the input box

[brian6932]

To delete to first/last word boundary. I have my termemu set to convert CTRL+BACKSPACE into CTRL+W anyway, so that specific case isn't as important I guess, but still good to support.

[Beastwick18]

This might be good to add since I had wanted the input box to vaguely match bash. I'm working on v0.10 which would allow for custom keybinds, but a 0.9.x version likely will come with this and some other features in the meantime.