Preserve additional metadata and produce a spec v2 META.json

This builds on the the prior pull req (#2) by additionally preserving the CPAN::Meta object in a cpan_meta attribute
and using that to generate a real META.json.

I expect backward compatibility is preserved this way
(as opposed to reworking the Module::Faker internals to be more v2-ish),
and frankly it's a lot less work :-)

Honestly I haven't read through a lot of the code to know what else Module::Faker is doing,
so this is a pretty naive modification.

Let me know if you think this is a good route to go on...
I could add some more testing and maybe read through the dist a little more to see what else is happening.

Also it would be fairly easy to expand this to generate the META.yml automatically
when there is cpan_meta object available.