C portability between non-UNIX o

[Doug Gwyn <gwyn>]

> <ctype.h>
>     int isalpha(int);
>     int tolower(int);
>     /* etc. */

I have always thought that there should be a tohostc() macro to
convert an ASCII character back to native host character set
(converse of toascii()).  Also, todigit() to map 3 to '3' and
tonumber() to map '3' to 3.  In other words, macros to support
writing PORTABLE atoi() functions etc.