Refactor Value and EvaluatorOutput models in order to get rid of optionals(?)

modules/system/src/main/kotlin/io/smnp/ext/function/ExitFunction.kt

@@ -13,7 +13,7 @@ class ExitFunction : Function("exit") {
    override fun define(new: FunctionDefinitionTool) {
       new function simple(optional(ofType(INT))) body { _, arguments ->
          val exitCode = arguments.getOrNull(0) ?: Value.int(0)
-         exitProcess(exitCode.value!! as Int)
+         exitProcess(exitCode.value as Int)
       }
    }
 }

modules/system/src/main/kotlin/io/smnp/ext/function/SleepFunction.kt

@@ -10,7 +10,7 @@ import io.smnp.type.model.Value
 class SleepFunction : Function("sleep") {
    override fun define(new: FunctionDefinitionTool) {
       new function simple(ofType(INT)) body { _, (milli) ->
-         Thread.sleep((milli.value!! as Int).toLong())
+         Thread.sleep((milli.value as Int).toLong())
          Value.void()
       }
    }