Add changelog.

CHANGELOG

@@ -0,0 +1,60 @@
+Release Notes
+=============
+
+v0.1.9
+------
+
+:Date: ???
+:Pull requests: 12, 13, 14
+
+- Numerous PEP8 fixes.
+- Add tests for unpack_pdu_objects.
+- Allow the validity period of submit_sm PDUs to be of variable length
+  (as required by section 4.4.1 of the SMPP v3.4 specification).
+- Add CHANGELOG and AUTHORS files.
+
+
+v0.1.8
+------
+
+:Date: 24 September 2015
+:Pull requests: 11
+
+- Move requirements into setup.py (they were in requirements.pip).
+- Add missing files to source distribution.
+- Fix name of license file.
+
+
+v0.1.7
+------
+
+:Date: 4 August 2015
+:Pull requests: None
+
+- Fix reading of requirements in setup.py.
+
+
+v0.1.6
+------
+
+:Date: 4 August 2015
+:Pull requests: None
+
+- Fix reading long description in setup.py.
+
+
+v0.1.5
+------
+
+:Date: 12 February 2015
+:Pull requests: 9
+
+- Fix reassembly of multipart messages.
+
+
+v0.1.4
+------
+
+:Date: 15 October 2014
+
+- Initial release.