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

Since the description about CPAN Meta file found the place which does not suit an actual code when writing the code of Pull-Request#77, I corrected.

Moreover, since the place where the coverage of a CPAN Meta file related test code is insufficient was found, I added. 

## 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.

## Improved the code coverage by adding test code for META.yml and META.json