add mysql::perl

An additional helper class to ensure that the Perl MySQL DBD driver is
installed (DBD::mysql).
mysql::perl tests
...and add mysql::perl to README.md
...and credit $self, too.

Why not?
Merge branch 'master' into topic/perl

Conflicts:
	manifests/init.pp
Merge pull request #187 from RsrchBoy/topic/perl

add mysql::perl helper class