reorganize module

_archive/rhai_engine/rhaibook/ref/methods.md

@@ -0,0 +1,18 @@
+Methods
+=======
+
+Data types may have _methods_ that can be called:
+
+> _object_ `.` _method_ `(` _parameters_ ... `)`
+
+A runtime error is raised if the appropriate method does not exist for the object's data type.
+
+
+Elvis Operator
+--------------
+
+The [_Elvis_ operator](https://en.wikipedia.org/wiki/Elvis_operator) can be used to short-circuit
+the method call when the object itself is `()`.
+
+> `// method is not called if object is ()`  
+> _object_ `?.` _method_ `(` _parameters_ ... `)`