fixing #113 and adding proper mouse support

[sminez]

Thanks to @favilo for the initial implementation that this was inspired by (found here) and apologies to @psychon for not addressing the issue with motion notify events until now...!

This change includes a breaking API change to how mouse bindings are defined: rather than bindings being tied individually to press, release and motion the MouseEventHandler trait now defines a handler that is responsible for all three for a given button press and modifier set. As a demonstration of how this looks, this is the simple mouse bindings that are now present in the minimal example:

fn mouse_bindings() -> HashMap<MouseState, Box<dyn MouseEventHandler<RustConn>>> {
    use penrose::core::bindings::{
        ModifierKey::{Meta, Shift},
        MouseButton::{Left, Middle, Right},
    };

    map! {
        map_keys: |(button, modifiers)| MouseState { button, modifiers };

        (Left, vec![Shift, Meta]) => MouseDragHandler::boxed_default(),
        (Right, vec![Shift, Meta]) => MouseResizeHandler::boxed_default(),
        (Middle, vec![Shift, Meta]) => sink_clicked(),
    }
}

mouse-support-demo-2024-06-22_17.03.08.mp4