Fix page offset miscalculation in instruction fetch

src/core.rs

@@ -38,7 +38,7 @@ impl Core {
     pub fn run(&mut self) {
         loop {
             let page = (self.pc / 4096) as usize;
-            let offset = (self.pc / 4) as u16;
+            let offset = (self.pc % 4096 / 4) as u16;
             if !self.pc.is_multiple_of(4) {
                 //replace eprint with logging, replace break with exception
                 eprintln!("PC not aligned");