feat: add support for waiting on notification click

[tasuren]

This PR solves issue #69. It adds the method click to Notification for waiting notification click.

Example of usage:

let response = send_notification(
    "clickable notification",
    None,
    "click me",
    Some(Notification::new().click(true)),
)
.unwrap();

The purpose of adding the click method to wait for notification click is to ensure backward compatibility. Otherwise, it would block a thread, but the developer might not realize that.

[hoodie]

sorry for the long wait. Thanks for the contribution, I think this is a good fit. I would like to rename the .click(bool) function however to something more explicit like ".wait_for_click().

[tasuren]

Thank you for your confirmation.
I agree, wait_for_click() is a much clearer name. I appreciate you making the change.