WorkdaysBetween: Fix issue when starting on a weekend.

The result was off by one when it started on either Saturday on Sunday. Another one that's worth noting is that $start->_wday actually has Sunday == 0.
WorkdaysBetween: Clearer way of computing the business days.

I also added a bunch of comprehensive tests.
WorkdaysBetween: Updated the output to change depending on the number of weekdays.

It would say "There is one workday ..." instead of "There is one workdays ...".
WorkdaysBetween: Support the shortened year format. Fixes #298.
WorkdaysBetween: Add the %m-%d-%y format.
WorkdaysBetween: Add "work days between" as a trigger.
WordaysBetween: Add "working days".

Thanks to @mintsoft for the suggestion.
WorkdaysBetween: Add support for full months such as "June 10, 2014".
WorkdaysBetween: Add tests for shortened years, too.
WorkdaysBetween: Add support for MM.DD.YYYY.
WorkdaysBetween: Revert to the old way of computing the dates.
WorkdaysBetween: Use a module to compute the dates instead.
Workdays: Add additional trigger word.
WorkdaysBetween: Make it always inclusive.
WorkdaysBetween: Fix tests.
Merge pull request #297 from duckduckgo/jag/release/workdays

Workdays: Prepared the IA for release.