Add missing date tests to SpecRunner
Add tests for start and completion dates in January and December

Because months in the Date constructor are zero-based, January = 0, December = 11
When passing "12" as the month, the constructor will create a date for January of
the next year.
Bugfix: Dates with month "12" were wrongly parsed

Months from string were directly passed to Date constructor.
Those months are in the range 1-12, but Date expects months in the range 0-11.
For dates with a month of 12, it was parsed as "month 0 of the next year"
Merge pull request #2 from bartlibert/master

Fix: Dates in December not correctly parsed