docfix: Pg and replication traits already exist!
fix bad pod link in Class.pm

 * PR #27 fixed a bad CPAN link in README.mkdn, but neglected to fix it in
   the source document, Class.pm.
switch from MooseX::Types to Type::Tiny
get rid of MooseX::Attribute::ENV
convert use Moose to use Moo
convert roles to Moo::Role