This is a collection of code taken from StackOverflow answers. The project is explained at http://stackoverflow.com/a/17537472/1737957
Like all contributions to StackOverflow, this project is licensed under cc-wiki with attribution required: http://creativecommons.org/licenses/by-sa/3.0/
All of the project is either the work of the various stackoverflow contributors in their replies, or my own work. Each class which implements IDateDifference is named with the username of the contributor in question. My contributions to these files are small and mechanical - changing the signatures of functions and so on to make them uniform.