macos: enable running lan-mouse on macos (#42)

* macos: initial support

- adapted conditional compilation
- moved lan-mouse socket to ~/Library/Caches/lan-mouse-socket.sock instead of XDG_RUNTIME_DIR
- support for mouse input emulation
TODO: Keycode translation, input capture

src/event.rs

@@ -3,6 +3,11 @@ use std::{
     fmt::{self, Display},
 };
 
+// FIXME
+pub(crate) const BTN_LEFT: u32 = 0x110;
+pub(crate) const BTN_RIGHT: u32 = 0x111;
+pub(crate) const BTN_MIDDLE: u32 = 0x112;
+
 #[derive(Debug, Clone, Copy)]
 pub enum PointerEvent {
     Motion {