Add Date Module

[DavePearce]

The benchmark 016_date provides a basic Gregorian date facility. We should extend and incorporate this.

[DavePearce]

What functionality should a datetime package provide?

• Ability to get current date and time (e.g. LocalDate.now())
• Ability to add a delta (e.g. date plus 5 days)
• Ability to compare date and times
• Ability to format dates for output in different ways
• Ability to handle timezones