enumeration value '...' not handled in switch

in unicode_width().

<Deuce> Unicode isn't encoding.
<Deuce> And petdefs.h is a mapping.
:-)

@U+<codepoint-in-hex>@ - automatic CP437 fallback char, if available
@U+<codepoint-in-hex|cp437char-in-hex>, specify CP437 fallback char
@U+<codepoint-in-hex!cp437char-in-hex>, specify CP437 fallback char
(used if no automatic fallback mapping is available)

Replaced unicode_is_zerowidth() with unicode_width(), in preparation for
"fullwidth" char support.
Added UNICODE_UNDEFINED definition (0x0000)
(UNICODE_NULL is already defined, at least in MSVC).

if (fg)
	FREE_AND_NULL(fd);
else
	FREE_AND_NULL(bg);

Since not *everything* that #include's sbbs.h needs the PETSCII defs,
remove it from sbbs.h and just #include petdefs.h where we need it.
The catch-all header file is a problematic organizational design and we are
moving away from that.

enum unicode_codepoint.
I got tired of looking up and cross-referencing all these damn numbers.

Disable the "Swap DEL/BBS key" question, by default (if the user sends
DEL, do the swap).
Beautify the backspace key prompt/report thing (add/remove blanks lines
mostly).

Disable the "Swap DEL/BBS key" question, by default (if the user sends
DEL, do the swap).
Beautify the backspace key prompt/report thing (add/remove blanks lines
mostly).

This means the JS global word_wrap() method has a new optional Boolean arg
as well.

user signature (.sig file) or editor created message tag (editor.tag file)
contents before adding to message base.

is defined (not defined by default).

I'm assuming Deuce meant to type '\x7f' instead of '\x1f'.
Replaced '\x1f' with the unambiguous DEL macro.

1. it didn't work (in the #if 0 block) because of checking the same char twice
2. Ctrl-A/Ctrl-A is no more special than Ctrl-A/Ctrl-B or Ctrl-A/Ctrl-Z
   (I think Deuce was thinking of Ctrl-A/A, but there are other printing
   Ctrl-A codes too, e.g. Ctrl-A/z).

fidodefs.h:47:27: warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
 #define FIDO_CHARSET_UTF8 "CHRS: UTF-8 4" /* FTS-5003 */
                           ^
writemsg.cpp:645:15: note: in expansion of macro 'FIDO_CHARSET_UTF8'
    *charset = FIDO_CHARSET_UTF8;

(e.g. applies to email and netmail now too).

utf8.c: In function 'utf8_getc':
utf8.c:327:7: warning: this 'else' clause does not guard... [-Wmisleading-indentation]
     } else
       ^~~~
utf8.c:329:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'else'
  if(val != NULL) {
  ^~