Improve socket discovery, handling, and logging

Implement the following logic:
* first try SWAYSOCK
* if failed, then try I3SOCK, the legacy one coming from i3
* if failed, then we abort with an error

src/main.rs

@@ -91,19 +91,35 @@ struct MoveAction {
 }
 
 fn get_stream() -> UnixStream {
-    let socket_path = match env::var("I3SOCK") {
+    for socket_var in ["SWAYSOCK", "I3SOCK"] {
+        let socket_path = match env::var(socket_var) {
             Ok(val) => val,
             Err(_e) => {
-            panic!("couldn't find i3/sway socket");
+                eprintln!("{} not found in environment", socket_var);
+                continue;
             }
         };
 
         let socket = Path::new(&socket_path);
 
         match UnixStream::connect(&socket) {
-        Err(_) => panic!("couldn't connect to i3/sway socket"),
-        Ok(stream) => stream,
+            Err(_) => {
+                eprintln!(
+                    "counldn't connect to socket '{}' found in ${}",
+                    socket_path, socket_var
+                );
+                continue;
             }
+            Ok(stream) => {
+                eprintln!(
+                    "successful connection to socket '{}' found in ${}",
+                    socket_path, socket_var
+                );
+                return stream;
+            }
+        }
+    }
+    panic!("couldn't find any i3/sway socket")
 }
 
 fn send_msg(mut stream: &UnixStream, msg_type: u32, payload: &str) {