work on string, bug fixes, overloaded assignment operator. Still need to get overloaded copy_construct for declaration assignment

tests/test_string.krak

@@ -5,6 +5,14 @@ import string;
 fun main(): int {
     var str.construct("hello strings"): string::string;
     io::println(str);
+    str = "assignment overload"
+    io::println(str);
+    io::println(str + "2");
+    str += " with additional"
+    io::println(str);
+    //var initilized:string::string = "hope"
+    //io::println(initilized)
+    //io::println(initilized+ "3")
     return 0;
 }