Calling Functions
Overview
These functions allows you to call any public function of any class
from a component. This function can be native, or written in Gambas.
First, you must use 
GB.GetFunction to retrieve sort of a function
pointer from the name of the function and the class it is declared in.
Then, you call the function by first pushing arguments on the
interpreter stack with 
GB.Push, and then effectively
executing the function with 
GB.Call.