Dist munging

Hi, I've done some minor changes to the distribution layout:
* test are to be stored in `t/` directory
* `Changes` file now satisfies `CPAN::Changes::Spec`. There is a special [online service](http://changes.cpanhq.org/author/BOWMANBS) to check your CPAN uploads for correctness of the changelog.

This PR is part of my [advent quest](https://questhub.io/realm/perl/quest/547b4202070ccf750d00010e).

Cheers,
Sergey