Time helper functions

[philrz]

As proposed by @mccanne:

In playing with times, I think we should take a little time to invest in helper functions, e.g., year(), month(), day().

[philrz]

Depending on what @mccanne had in mind when he made the statement above, the strftime function added in #5197 might cover this since the directives allow extracting things like the year, month, and day portions of time values.