[DEV] open new 1.6 development branch

This new branch is based on 1.5.0, which 1.6-dev0 is 100% equivalent to.
The README has been updated to mention that it is a development branch.

Released version 1.6-dev0 with the following main changes :
    - exact copy of 1.5.0
diff --git a/CHANGELOG b/CHANGELOG
index a893627..f17e680 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,9 @@
 ChangeLog :
 ===========
 
+2014/06/19 : 1.6-dev0
+    - exact copy of 1.5.0
+
 2014/06/19 : 1.5.0
     - MEDIUM: ssl: ignored file names ending as '.issuer' or '.ocsp'.
     - MEDIUM: ssl: basic OCSP stapling support.