Add new example scripts.

scripts/function_decl4.rhai

@@ -0,0 +1,12 @@
+// This script defines a function that acts as a method
+
+// Use 'this' to refer to the object of a method call
+fn action(x, y) {
+    this = this.abs() + x * y;      // 'this' can be modified
+}
+
+let obj = -40;
+
+obj.action(1, 2);                   // call 'action' as method
+
+print(`obj should now be 42: ${obj}`);