Built in function "save": Implement default file name.

Implement a default file name for the built in "save" function.

The "save" implementation in the run time library has a default file name that is derived from the class name. The dummy implementation in the Interpreter has no default value.
The "save" implementation in the run time library has a default file name that is derived from the
class name. The dummy implementation in the Interpreter has no default value.

Problems:
* The code that creates the Siml-Signature can not extract the default values from the function
 * The code that creates the Siml-Signature can not extract the default values from the function definition.
  definition.
* The type testing is too simple: String | NONE (String or special value NONE) can not be
 * The type testing is too simple: String | NONE (String or special value NONE) can not be expressed.
   expressed.