Update changelog

CHANGES.md

@@ -1,3 +1,21 @@
+0.6 2018-05-29
+--------------
+
+- Add a parameter `version` to `Dblib.connect` to be able to choose
+  the protocol version.  Explain how the old protocol versions
+  do not allow empty strings which will be returned as `' '`.
+- Keep the compatibility with FreeTDS version < 0.91.
+- Keep int64 as such on the OCaml side (they used to be transformed
+  into strings).
+- Document `Dblib.severity`.
+- Make error messages more informative by splicing the binding on a
+  finer level.  A configure script ensures the synchronization with
+  values defined in the C header files.
+- Add tests for `Dblib` and `Ct` (checked by AppVeyor on
+  Windows/mingw).
+- Improve the interface of `Ct.get_messages`.
+- Complete the depexts list.
+
 0.5.2 2018-04-15
 ----------------