Add support for microseconds to `Date` and `DateTime` and `TimeOfDay`.

[jmalloc]

• Add DateTime::microsecond()
• Add DateTime::differenceAsMicroseconds()
• Add DateTime::fromComponents() static factory method (do not change original constructor as this is a BC break to be handled in Update DateTime and TimeOfDay constructors to accept microseconds parameter. #85)
• Add TimeOfDay::microsecond()
• Add TimeOfDay:fromComponents() static factory method (do not change original constructor as this is a BC break to be handled in Update DateTime and TimeOfDay constructors to accept microseconds parameter. #85)
• Add Date::differenceAsMicroseconds()

Do not change interfaces as this is a BC break to be handled in #86.