Improved the pod about the description of CPAN Meta file (META.yml and META.json).

1. Detailed the content of an outputs to CPAN Meta file at the time of specifying ver 2.0 as meta-spec especially for ExtUtils::MakeMaker.
2. Added the description about the META.json for ExtUtils::MM_Any.
Added the insufficient test code and improved code coverage.
Merge pull request #79 from magnolia-k/master

Improved the pod about the description of CPAN Meta file and the code coverage by adding test code.