Added a learning test for interval
DateInterval
Added learning test for Facebook birthday field
Interval Specification must starts with P
Added class DateIntervalPeriodDesginator
Added constructor
Test behavior from DateTime and DateInterval code style.
Test cloning objects in php.
Bla bla bla
Improved readability of code.
A way to test.
Entity has states.
Count statuses.
Default state.
Refactoring.
Get current status.
Entity can change status.
Covered all staus change.
Refactored tests and added README.md.
Fixed DateInterval.