Command Line Argument parsing module  for C02 Programs

This is module provides functions for parsing command line arguments
passed into a program.

Although 6502 based computers rarely use a shell interface, this module
allows arguments to be specified when executing a program on several
popular systems.

On the Apple I, the syntax is

  0300R arg1 arg2 arg3 ...
  
and on Commodore computers, the syntax is

  RUN:"arg1 arg2 arg3 ...

At the beginning of the program use the directives

  #include <stddef.h02>
  #include <args.h02>

The following functions are defined:

  r = argset();         Sets up argument list for parsing. This function
                        must be called only once and before any calls to 
                        the argget() function.

                        Returns 0 if successful, or 255 if no argument
                        list was specified or argument parsing is not
                        supported. 
                        
                        A result of success does not necessarily mean that
                        any arguments were passed, only that the program
                        was executed using the appropriate syntax.
                       
  n = argget(&s);       Reads the next argument into string s. 

                        Returns the length of the argument. After the 
                        last argument, sets s to an empty string and 
                        returns 0.

                        Note: Sets dstptr to the address of s.

Note: This library expects the following functions to be defined:

  setdst();             Set destination pointer.

along with the zero page variable
  
  dstptr                Destination pointer.

the variables
  
  sysbfr                System buffer              
  sysbfp                System buffer position.

and the constant
  
  #SYSBFL               System buffer length.