Background service (#43)

better handling of background-service: lan-mouse can now be run without a gui by specifying --daemon as an argument.
Otherwise the servic will be run as a child process and correctly terminate when the window is closed / frontend exits.

Closes #38

src/producer.rs

@@ -1,4 +1,5 @@
-use std::{error::Error, io};
+use anyhow::Result;
+use std::io;
 
 use futures_core::Stream;
 
@@ -15,7 +16,7 @@ enum Backend {
     X11,
 }
 
-pub fn create() -> Result<Box<dyn EventProducer>, Box<dyn Error>> {
+pub async fn create() -> Result<Box<dyn EventProducer>> {
     #[cfg(windows)]
     return Ok(Box::new(producer::windows::WindowsProducer::new()));