Porting/corelist-perldelta.pl - Use Module::CoreList in dist/

Ensure that the latest version of Module::CoreList is used when
running the script
Porting/corelist-perldelta.pl - fix usage example

lib needs to be included when generating the module changes
with the currently build Perl
Porting/corelist-perldelta.pl - Remove trailing whitespace
Porting/corelist.pl - DeltaParser: match modules in L<> and C<>

Module names have been listed in both
Porting/corelist-perldelta.pl - Improve version parsing

Catch more forms of how updated modules have been listed in past
perldelta
Porting/corelist-perldelta.pl - Cleanup DeltaParser

* Comment generation of accessor methods
* Make _parse_delta() more explicit by calling the section parsing
  methods explicitly
* Ensure that the new_modules, updated_modules, and removed_modules
  attributes exist even if the perldelta file does not contain the
  corresponding sections
Porting/corelist-perldelta.pl - Improve corelist_delta

corelist_delta now goes through almost all of the core distributions.
The problem with the previous approach was that the keys of %Modules in
Porting/Maintainers.pl do not all correspond to a valid distribution or
do not correspond to a module as listed in Module::CoreList.
This commit also updates the callers of the function.
Porting/corelist-perldelta.pl - Make do_check less noisy

The removed modules as returned by corelist_perldelta contains
too many false positives to be useful. Also, explictly state
whether the difference is from the pod or the results returned from
corelist_perldelta().
Porting/corelist-perldelta.pl - Add a new mode update

This adds a new mode, update, which given an the path to an existing
perldelta file, will add missing entries and update incorrect version
information.

This commit introduces a new module, DeltaUpdater, which is used
for pod manipulation.
Porting/corelist-perldelta.pl - Make do_generate use DeltaUpdater

DeltaUpdater::sections_to_pod() makes generate_section() redundant
Porting/corelist-perldelta.pl - Default to comparing last two versions

do_update_existing() previously required versions to be specified
Porting/corelist-perldelta.pl - Use Unix newlines in perldelta
Porting/corelist-perldelta.pl - Skip dummy items during update
Porting/corelist-perldelta.pl - Make documentation clearer

* Fix incorrect usage example for update
* Document that removed modules are currently ignored
* Clarify why some distributions have to be manually checked
* Clarify why a distribution may not be listed in Module::CoreList
Add Abir Viqar to AUTHORS
Update various instructions about the use of Porting/corelist-perldelta.pl
Porting/corelist-perldelta.pl - Minor tidy-ups
Merge branch 'perldelta' into blead

Add a new mode to Porting/corelist-perldelta.pl to update the module
changes in pod/perldelta.pod for the perl you are currently building.

This can be run as:

./perl -Ilib Porting/corelist-perldelta.pl --mode=update pod/perldelta.pod

*after* updating Module::CoreList with something like:

./perl -Ilib Porting/corelist.pl cpan

There is still scope for improvement in the handling of removed modules,
and in automatically cribbing information from the Changes files of those
modules that have been updated, but this is a big step in the right
direction.