Optimization of string and vector with references and less functional code, bugfix of closing over references

tests/test_close_over_references.krak

@@ -0,0 +1,17 @@
+import io:*
+
+fun func(it: ref int) {
+    it++
+    fun() {
+        it++
+        println(it)
+    }()
+}
+
+fun main(): int {
+    var it = 7
+    func(it)
+    println(it)
+
+    return 0
+}