Add primitive types to String conversion. (#50)

backend.native/tests/runtime/basic/tostring0.kt

@@ -0,0 +1,14 @@
+fun main(args : Array<String>) {
+    println(127.toByte().toString())
+    println(255.toByte().toString())
+    println(239.toShort().toString())
+    println('A'.toString())
+    // println('Ё'.toString())
+    // println('ト'.toString())
+    println(1122334455.toString())
+    println(112233445566778899.toString())
+    println(1e27.toFloat().toString())
+    println(1e-300.toDouble().toString())
+    println(true.toString())
+    println(false.toString())
+}