Updating support for the Interval primitive

This change updates the Interval primitive, adding a fresh
implementation and documentation. A new unit test suite for the
primitive is included.

kmip/core/exceptions.py

@@ -21,6 +21,14 @@ class InvalidKmipEncoding(Exception):
     pass
 
 
+class InvalidPaddingBytes(Exception):
+    """
+    An exception raised for errors when processing the padding bytes of
+    primitive encodings.
+    """
+    pass
+
+
 class InvalidPrimitiveLength(Exception):
     """
     An exception raised for errors when processing primitives with invalid