Add when concept

[kahgoh]

This adds the when concept for Kotlin. Also took the opportunity to fix the name for the "Log Levels" exercise.

@SleeplessByte, this is ready for review

[SleeplessByte]

Suggested change

	It is similar to `switch` in Java, but more flexible than a chain of `if` ... `else if` ... `else`.
	It is similar to `switch` in Java, and more flexible than a chain of `if` ... `else if` ... `else`.

[SleeplessByte]

So this is pattern matching then?

Could be something to call out!

[kahgoh]

Added mention about pattern matching.

[SleeplessByte]

Does regexp work?

[kahgoh]

Yeah, regexp can work as part of the guard. Something like this:

val code = 3
val classification = "animal"
val type = when (code) {
    3 if """.*mal""".toRegex().matches(classification) -> "animal"
    else -> "unknown"
}

But if using it match the value, I think you can only do it by matching conditions (i.e. without a value to match). For example:

val classification = "animal"
val type = when {
    Regex("''.*mal""").matches(classification) -> "animal"
    Regex(''"fru.*""").matches(classification) -> "fruit"
    else -> "unknown"
}

[kahgoh]

Oh, I just learn I can indeed use Regexp but would need to define an extension function:

operator fun Regex.contains(text: CharSequence): Boolean = this.matches(text)

fun main() {
    val classification = "animal"
    val res = when(classification) {
        in Regex(""".*mal""") -> println("animal")
        in Regex("""fru.*""") -> println("fruit")
        else -> println("unknown")
    }

    println(res)
}

[kahgoh]

Added something about this in the about.md.

[SleeplessByte]

Suggested change

	It is similar to `switch` in Java, but more flexible than a chain of `if` ... `else if` ... `else`.
	It is similar to `switch` in Java, and more flexible than a chain of `if` ... `else if` ... `else`.

[SleeplessByte]

Suggested change

	- If the guess is `41` or `43` and there have been less than : "So close"
	- If the guess is `41` or `43` and there have been no more than 5 guesses: "So close"

[SleeplessByte]

Suggested change

	It is similar to `switch` in Java, but more flexible than a chain of `if` ... `else if` ... `else`.
	It is similar to `switch` in Java, and more flexible than a chain of `if` ... `else if` ... `else`.