CMSP 15. Add development_requires

15. Add development_requires

Proposal:

The development_requires field should specify all prerequisites only needed
during development. For example this could include templating or other
preprocessing modules needed to generate the final source. (Slaven Rezic)

Comments:

* This would be just convenience for developers, not for the end users. But
it happens to be more and more popular to either take over other people's
modules, or to fork distributions directly from repositories for
patching, so it would be nice to have a concise notation to specify also
the developer's prereqs.

* So one can just write

cpan `perl -MYAML::Syck -e '$meta = LoadFile shift;
for (qw(configure_requires requires development_requires ...))
{ print join "", map { "$_\n" } keys %{ $meta->{$_} || {} } } ' META.yml`

and has everything he needs.