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/backend/consumer/windows.rs

@@ -1,4 +1,3 @@
-use anyhow::Result;
 use async_trait::async_trait;
 use crate::{event::{KeyboardEvent, PointerEvent}, consumer::EventConsumer};
 use winapi::{

src/backend/producer/libei.rs

@@ -1,4 +1,5 @@
-use std::{error::Error, io, result::Result, task::Poll};
+use anyhow::Result;
+use std::{io, task::Poll};
 
 use futures_core::Stream;
 
@@ -7,7 +8,7 @@ use crate::{producer::EventProducer, event::Event, client::ClientHandle};
 pub struct LibeiProducer {}
 
 impl LibeiProducer {
-    pub fn new() -> Result<Self, Box<dyn Error>> {
+    pub fn new() -> Result<Self> {
         Ok(Self {  })
     }
 }