first line of help string of each code includes option prefix

[Ed Bueler]

c/ch2/tri.c is an example. Make this uniform so that

$ ./program -help |head          # determine that "prg_" is prefix
$ ./program -help |grep prg_     # list the options with this prefix

is part of the "help system".

Then document this feature in Chapters 2 and 3 where it will first be used.

[Ed Bueler]

I still need to go through and make this uniform.

[Ed Bueler]

I believe this is done enough.