Implementation of Discordian Chronology

[robfletcher]

I've updated the implementation to conform to the slightly different interface. Specifically plus and the 2 overloaded versions of periodUntil are new from the implementation I did originally for the ThreeTen/threetenbp project.

[jodastephen]

Looks good. I just need to establish the licensing. Are you willing to license this under the same terms (BSD 3 clause) as the rest of the threetenbp-extra project, effectively assigning copyright to myself and Michael. This can be done by adding a license header to the three files in your copy. Thanks.

[robfletcher]

Sorry, I keep forgetting to do this! Of course, I'm happy to assign copyright. I've also added an @author tag to the javadocs on the classes, hope that's ok. If not feel free to remove.

[jodastephen]

Thanks, I'll try to get around to merging this soon...