Add Travis CI config

The `cpanfile` duplicates some information in `Makefile.PL` but a `cpanfile` is the default way for Travis CI to handle [dependency management][1] (via `cpanm`).  The `cpanfile` also enables use of [Carton][].

Perl 5.14 and 5.16 are disabled because they were failing.  See my Travis CI failures: [Build 1][] and [Build 2][].  We should make an issue acknowledging this potential problem with 5.14 and 5.16.

[Carton]: https://metacpan.org/release/Carton
[1]: http://docs.travis-ci.com/user/languages/perl/#Dependency-Management
[Build 1]: https://travis-ci.org/nnutter/nessy-client-perl/builds/21615380
[Build 2]: https://travis-ci.org/nnutter/nessy-client-perl/builds/21615574