"richtext.c" may be used as a library in another program, by defining the
macro RICHTEXT_LIBRARY when it is compiled and calling the function
"richtext_main(argc, argv)" with the arguments set to the normal richtext
command-line arguments.  It is also necessary to link with "richlex.c",
"richset.c", "usascii.c" and "iso2022.c" which provide services to
"richtext.c".