ARX.O, RARX.O, PARX.O, QARX.O - C runtime startup modules

	These do various things: most of them parse the command line into
separate args, all of them load the stack pointer to the top of free memory,
and set up argc & argv for procedure main. They then call main, and on
return exit to the system (or in the case of PARX.O execute the next program
in the pipe). In addition, they all define an external label exit which can
be jumped to in order to terminate the program with extreme prejudice. The
difference between them is how clever they are. In order of increasing
intelligence we have:

	QARX.O	(Q for quick): ignores the command line args - does no
		argc/argv setup at all.

	ARX.O	parse the command line into arguments, argv is set up from
		these, however the program name is not available as argv[0].
		argc is set as needed.

	RARX.O	(R for redirection): parse the command line, but if it finds
		arguments with a leading < > or >> these don't reach argv,
		instead they are used to do redirection of standard input
		& output just like UNIX does it, to give an example,
		A>PROG
		normally PROG would take standard input from the keyboard,
		and send standard output to the screen, however if it
		were invoked as follows:
		A>PROG <FILE1 >FILE2
		standard input would read from FILE1, and FILE2 would be
		created to hold the standard output, in addition
		A>PROG >>FILE3
		will send output to FILE3, but if the file exists it is
		opened for append rather than being created anew.

	PARX.O	(P for pipe): does all that RARX.O does, it also will look for
		| chars in the command line, and do pipes like UNIX does, so

		PROG | PROG1 | PROG2

		will work. A few words of warning are in order here: because
		the Z80 is not the worlds biggest CPU, I haven't figured out
		a way to do multi-tasking (but I'm working on it (?!?!)). As
		a result of this, each program in the pipe must finish before
		the next one can start, requiring that all the information
		passing from one to the next be stored on disk: so if you do a

		CAT *.Z | ...

		you may find yourself in a lot of trouble when CAT runs out of
		room to save all the stuff that was in *.Z. It goes without
		saying that all programs in the pipe EXCEPT THE LAST must have
		been linked with PARX, and the last needs either PARX or RARX:
		the reason being that in the first example, PROG1 would be
		invoked with a command line looking like:

		PROG1 <TEMPFILE | PROG2

	Note that none of these routines which do set up arguments will set
up the program name as argv[0] as is conventional under UNIX, instead argv[0]
is set to the null string, i.e. a pointer to a zero byte.


	For those who have not worked with UNIX this (hopefully) will give
a consise overview of exactly what argc and argv are:

A>PROGRAM ARG1 ARG2

argv (word) ---->   argv[0] - argv[1] - argv[2]   argc is 3 - 3 arguments
[argument	       |	 |	   |	  [argument count max]
 vector]	       |	 |	   v
		       |	 |	   second arg string
		       |	 v
		       |	 first arg string
		       v
		       normally program name, not available under CP/M


The way I set these up is to use the command line tail saved by CP/M
at location 0x80 - as an example:

A>PROGRAM ARG1 ARG2

would leave

0080:  0A 20 41 52 47 31 20 41-52 47 32 00 00 00 00 00   . ARG1 ARG2.....

in memory. After ARX has done its stuff, the following will be elsewhere
in memory:

   high in memory
argv[3]		NULL pointer (i.e. zero word)
argv[2]		0x87 - address of ARG2 string (terminated by zero byte)
argv[1]		0x82 - address of ARG1 string
argv[0]		pointer to a zero byte (not the NULL pointer)
   lower in memory

and on the stack will be found:

start of stack (high in memory)

argv		address of argv[0] whereever it is in memory
argc		3 in this case - three valid arguments
return address	return as created by the call to main

end of stack (lower in memory)

Usually spaces (and some other chars) can be a problem to get into command
line arguments, so the following 'escape' sequences are recognised - using
backslash '\' as the lead in character:

'\ '	backslash space - gets converted to a space, allow spaces to
		get into arguments, usually spaces are used to separate
		arguments

'\t'	backslash 't' - gets converted to a tab

'\n'	backslash 'n' - gets converted to a linefeed (newline)

'\r'	backslash 'r' - gets converted to a carriage return

'\b'	backslash 'b' - gets converted to a backspace

'\f'	backslash 'f' - gets converted to a formfeed

'\\'	backslash backslash - gets converted to a single backslash

'\e'	backslash 'e' - gets converted to an escape (may not be
		implemented yet)