Added System initializer method

src/kernel/system.rs

@@ -28,6 +28,17 @@ pub struct System {
 
 impl System {
 
+    /// System constructor
+    pub fn new(machine: Machine, scheduler: Scheduler) -> Self {
+        Self {
+            g_machine: machine,
+            g_current_thread: None,
+            g_thread_to_be_destroyed: None,
+            g_alive: List::new(),
+            g_scheduler: scheduler
+        }
+    } 
+
     // GETTERS
 
     /// Returns the Machine