Support terminal resizing (MacOS, Linux only)

[keynmol]

We can use signals (SIGWINCH) and two threads to handle resizing.

Here's a simple gist where I tested that it works: https://gist.github.com/keynmol/e5322a01c85edfa521fe5f6aebb2bef6

We will need to run the input provider on a separate thread.

We should add another group of events – Event.TerminalChange(size = WindowSize(width = ..., height = ...)), and add an optional WindowSize parameter to Event.Init, so that the prompt can optionally size itself accordingly to the window size.

This will involve some non-trivial logic in fitting the text on the screen horizontally, potentially splitting it in multiple lines (depends on #43)