Add utilities related to java.time.Duration

[sleberknight]

Because I've recently been dealing with Duration a lot, and having to check whether positive or positive or zero, I created a discussion ( #1217 ) on whether to create our own KiwiDurations utility. Admittedly, it would contain some pretty trivial methods. But after writing:

if (!duration.isNegative() && !duration.isZero()) { ... }

and even:

if (!duration.isNegative()) { ... }

several times, I wanted this instead:

if (duration.isPositive()) { ... }

and

if (duration.isPositiveOrZero()) { ... }

Why? First, having to write a compound boolean expression that negates each individual expression is annoying, especially when you do it many times (or even twice). Second, compound expressions are more difficult to read when skimming code, especially when each one has a ! in front of it (it's easy to miss them).

Since this library isn't Kotlin or a language supporting extension methods, I clearly can't modify the JDK's Duration class. So, I guess we'll just have to do with:

if (KiwiDurations.isPositive(duration)) { ... }

and

if (KiwiDurations.isPositiveOrZero(duration)) { ... }

With static imports it's nicer - just isPositive(duration).

While we're at it, might as well support the other missing option:

if (KiwiDurations.isNegativeOrZero(duration)) { ... }

So, that's three simple, but useful and easier to read in my opinion, methods:

• isPositive(Duration)
• isPositiveOrZero(Duration)
• isNegativeOrZero(Duration)