embed.fnc: Clarify m flag behavior comment
sv.c: Silence VMS compiler warning

The result of this must be at least 0 as the type is unsigned, so
the compiler gives a warning.
regcomp.c: Use available mnemonics for dumping regex

Perl supports \e and \b (in bracketed character classes).  Use these on
outputting like we do \t and \n, instead of a hex value
regcomp.c: white-space only

Bring two case statements into line with their peers
regcomp.c: Extract some code into a macro

This is in preparation for it to be used in more than one place
handy.h, regcomp.c: Add, clarify comments
regen/unicode_constants.pl: Find max ascii print cp

This creates a #define that gives the highest code point that is an
ASCII printable.  On ASCII-ish platforms, this is 0x7E, but on EBCDIC
platforms it varies, and can be as high as 0xFF.  This is in preparation
for needing this value in a future commit in regcomp.c
perldiag: Add clarification.
regcomp.c: Add 'const' to parameter
regcomp.c: Use symbolic constant instead of number

This is in preparation for it to be used in more than one place.
Improve -Dr output of bracketed char classes

I look at this output a lot to verify that patterns compiled correctly.
This commit makes them somewhat easier to read, while extending this to
also work on EBCDIC platforms (as yet untested).

In staring at these over time, I realized that punctuation literals are
mostly what contributes to being hard to read.  [A-Z] is just as
readable as [A-Y], but [%!@\]~] is harder to read than if there were
fewer.  Sometimes that can't be helped, but if many get output,
inverting the pattern [^...] can cause fewer to be output.  This commit
employs heuristics to invert when it thinks that that would be more
legible.  For example, it converts the output of [^"'] to be

 ANYOF[^"'][{unicode_all}]

instead of

 ANYOF[\x{00}-\x{1F} !#$%&()*+,\-./0-9:;<=>?@A-Z[\\\]\^_`a-z{|}~\x{7F}-\x{FF}][{unicode_all}]

Since it is a heuristic, it may not be the best under all circumstances,
and may need to be tweaked in the future.

If almost all the printables are to be output, it uses a hex range, as
that is probably more closely aligned with the intent of the pattern
than which individual printables are desired.  Again this heuristic can
be tweaked.

And it prints a leading 0 on things it outputs as hex formerly as a
single digit \x{0A} now instead of \x{A} previously.