Merge pull request #238 from metomi/prepare-3.1.0

Prepare release: 3.1.0

Merge pull request #206 from metomi/prepare-3.0.0

Prepare release: 3.0.0

Merge pull request #170 from MetRonnie/release

Update changelog

isodatetime release 13.

isodatetime release 12. Python 3 port.

isodatetime release 11

isodatetime release 10

isodatetime release 9

isodatetime release 8

isodatetime 2017.02.0. Release 7.