Refactor the "check categories and severity" logic in diag.t

Move the "todo" bailout as early as possible, before any work is done.
Replace C<use 5.01> [sic] with C<use feature 'state'>, as this makes the
intent much clearer.
Use parenthesis for like() and is() as this is consistent with the rest of the
test, and permits a simplification of the BEGIN handling.
Avoid VMS running autodoc.pl twice for no reason.

Previous descrip_mms.template carried separate rules to build perlintern.pod
and perlapi.pod, each of which caused autodoc.pl to run. autdoc.pl builds
both files when it runs, so this was duplicate work.
In t/porting/diag.t, use TestInit to chdir and set up @INC.

Also eliminate the $|=1, as it's really not necessary for tests that neither
fork nor shell out to other processes.
t/porting/diag.t now uses regen/embed_lib.pl to parse embed.fnc

Previously it had its own custom parsing code for embed.fnc.
In regen/regen_lib.pl, add 'Pod' as a third supported 'language'.

Pod needs a commenting style distinct from C and Perl. (ie the empty string)
Refactor autodoc.pl to use regen_lib.pl to generate file headers & footers.

This reduces duplication of code that generates '-*- buffer-read-only: t -*-',
'ex: set ro:' etc.
autodoc.pl now uses regen/embed_lib.pl to parse embed.fnc

Previously it had its own custom parsing code for embed.fnc.
Refactor autodoc.pl to read MANIFEST line by line, instead of slurping it.
Sync Module-CoreList version in Maintainers.pl
typo fixes for win32 scripts
typo fix for util script
typo fix for os2 module

Bump $VERSION for os2/OS2/OS2-Process/Process.pm.
making DOS stand out in dosify
typo fixes for porting pod note optimiser

Change to optimizer to be consistent with other uses of optimizer in todo.
Clear up confusion in regex optimizer entry.
typo fixes for porting modules

Bump $VERSION for Porting/Maintainers.pm.
Make t/podcheck.t less sensitive

The max line length is increased to 100.  This eliminates dozens of
known issues.

The warnings about using F<> and L<> instead of C<> have been removed
on the rationale that they are too opinionated.  They flag stylistic
issues rather than syntactic or structural issues and have minimal
impact on the effectiveness of the resulting documentation.
stop t/podcheck.t from flagging blockquotes
help t/podcheck.t skip duplicate pod in utils
fix various Pod line length warnings
fix various podcheck nits