Distribution Improvements

These commits fix errors that were preventing the distribution from being installed. These fixes include:
* Listing the dependencies in Makefile.pl
* Updating the manifest to include all necessary files
* Adding MANIFEST.SKIP to pass t/manifest.t
* Making t/pod-coverage.t an author test to allow end user installation

I also added the Github repository to Makefile.pl so that both search.cpan.org and metacpan.org will display a link to it.