Fix for implied dt-end and a failing unit test

This should fix issue #43.

Additionally, I noticed unit test "testYYYY_MM_DD__HHpm" was failing because mf2-php did not convert "9pm" to "21:00" properly. I did not see any time conversion function so I took the liberty of adding one, and unit tests for it. Let me know if any adjustments need to be made.