POD and CI

I'd like to browse the documentation on CPAN as hypertext, so I added links to all package names. I further add `.travis.yml` to enable public continuous integration with travis and coveralls:

[![Build Status](https://travis-ci.org/gbv/Catmandu.png?branch=master)](https://travis-ci.org/gbv/Catmandu)
[![Coverage Status](https://coveralls.io/repos/gbv/Catmandu/badge.png?branch=master)](https://coveralls.io/r/gbv/Catmandu?branch=master)

Just enable Catmandu in your travis and coveralls accounts to update build tests on every push.