Set up to start 0.7 development.

ChangeLog

@@ -1,3 +1,6 @@
+UNRELEASED Version 0.7.0
+    - 
+
 2017-05-30 Version 0.6.2
     - Fixed problem with header folding that caused the first line to be
       folded too long (Updated test test_add_body_length since l= tag is no

setup.py

@@ -24,7 +24,7 @@
 from distutils.core import setup
 import os
 
-version = "0.6.2"
+version = "0.7.0"
 
 setup(
     name = "dkimpy",