moved structs to their own files

added time since last state change

src/target_state.rs

@@ -0,0 +1,21 @@
+use std::net::Ipv4Addr;
+use std::time::SystemTime;
+
+#[derive(Clone)]
+pub struct TargetState {
+    pub target: Ipv4Addr,
+    pub alive: bool,
+    pub last_rtt: u32,
+    pub last_alive_change: SystemTime
+}
+
+impl Default for TargetState {
+    fn default() -> Self {
+        TargetState {
+            target: Ipv4Addr::new(127, 0, 0, 1),
+            alive: false,
+            last_rtt: 0,
+            last_alive_change: SystemTime::now()
+        }
+    }
+}