mktables: Add comments to output tables
regcomp.c: Rmv inaccurate and tangential comment

This comment contained inaccuracies and referred to behavior that has
been removed from the core for years.  isPRINT() is sufficiently
documented elsewhere to not need to have its use justified here.

I considered moving part of it to perlebcdic, but it's not generally
true: it's not true for one of Perl's supported EBCDIC code pages, for
example.
utf8.c: Remove hard-coded names.

The names of these hashes stored in some disk files is retrievable by a
standardized lookup.  There is no need to have them hard-coded in C
code.  This is one less opportunity for the file and the code to get out
of sync.
perlapi: Grammar nits

"The" referring to a parameter here does not look right to me, a native
English speaker.
utf8.h: Add parameter checking to some macros in DEBUGGING builds

This change should catch some wrong calls to these macros.  The meat of
the macros is extracted out into two internal-only macros, and the other
macros are rearranged to call these.
utf8.c: White-space only

Rearrange this multi-line conditional to be easier to read.