hamming: standardize starter implementation

exercises/hamming/src/main/java/Hamming.java

 public class Hamming {
+
+    Hamming(String leftStrand, String rightStrand) {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
+    int getHammingDistance() {
+        throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
+    }
+
 }