- Continued refactoring of address decoding.

- Device read and write may now throw MemoryAccessException, and appropriate
  throws clauses have been added throughout the code.

src/main/java/com/loomcom/symon/devices/Device.java

@@ -29,13 +29,17 @@ public abstract class Device implements Comparable<Device> {
   }
 
   /* Methods required to be implemented by inheriting classes. */
-  public abstract void write(int address, int data);
-  public abstract int read(int address);
+  public abstract void write(int address, int data) throws MemoryAccessException;
+  public abstract int read(int address) throws MemoryAccessException;
   public abstract String toString();
 
   public void setBus(Bus bus) {
     this.bus = bus;
   }
+  
+  public Bus getBus() {
+    return this.bus;
+  }
 
   public MemoryRange getMemoryRange() {
     return memoryRange;