Added digest interface and implementation

src/main/java/meerkat/crypto/Digest.java

@@ -0,0 +1,7 @@
+package meerkat.crypto;
+
+/**
+ * Created by talm on 11/9/15.
+ */
+public interface Digest {
+}

src/main/java/meerkat/crypto/concrete/SHA256Digest.java

@@ -0,0 +1,7 @@
+package meerkat.crypto.concrete;
+
+/**
+ * Created by talm on 11/9/15.
+ */
+public class SHA256Digest {
+}