Need to make event variable name configurable

[frame-lang]

Currently event name is hardwired to 'e' which disallows 'e' being used as an identifier. This example overwrites event e with an int.

    def __fibonaccidemo_state_PrintNextFibonacciNumber(self, e):
        if e._message == "next":
            e  = self.__compartment.state_args["c"] + self.__compartment.state_args["d"]
            print(e)
            (self.__compartment.state_args["c"]) = self.__compartment.state_args["d"]
            (self.__compartment.state_args["d"]) = e
            return
    
    ```