Add native coroutines example

[AAkira]

closes #56, #69

Run background thread

You can use this library on a background thread on iOS using Kotlin.coroutines as native-mt.

• Define scope

internal val mainScope = SharedScope(Dispatchers.Main)

internal val backgroundScope = SharedScope(Dispatchers.Default)

internal class SharedScope(private val context: CoroutineContext) : CoroutineScope {
    private val job = Job()
    private val exceptionHandler = CoroutineExceptionHandler { _, throwable ->
        println("[Coroutine Exception] $throwable")
    }

    override val coroutineContext: CoroutineContext
        get() = context + job + exceptionHandler
}

• usage

backgroundScope.launch {
    suspendFunction()
}