Add two abstraction helpers

Author: nima

digest.go

@@ -140,11 +140,21 @@ func (d Digest) Encoded() string {
 	return string(d[d.sepIndex()+1:])
 }
 
-// Hex is deprecated. Please use Digest.Encoded.
+// IsIdenticalTo compares this digest to any other, inclusive of the hashing algorithm used
+func (d Digest) IsIdenticalTo(o Digest) bool {
+	return string(d) == string(o)
+}
+
+// Deprecated: Hex has been deprecated in favor of Digest.Encoded
 func (d Digest) Hex() string {
 	return d.Encoded()
 }
 
+// IsEmpty does what it says (an empty digest is an empty string)
+func (d Digest) IsEmpty() bool {
+	return len(d.String()) == 0
+}
+
 func (d Digest) String() string {
 	return string(d)
 }