Allow input capture & emulation being disabled (#158)

* Input capture and emulation can now be disabled and will prompt the user to enable again.

* Improved error handling to deliver more useful error messages

input-event/src/lib.rs

@@ -5,6 +5,9 @@ pub mod error;
 pub mod proto;
 pub mod scancode;
 
+#[cfg(all(unix, feature = "libei", not(target_os = "macos")))]
+mod libei;
+
 // FIXME
 pub const BTN_LEFT: u32 = 0x110;
 pub const BTN_RIGHT: u32 = 0x111;