Added two checkers for Puppet's DSL.

The first checker, `puppet-parser`, uses puppet's own
`puppet parser validate` command to check syntax.

The second checker, `puppet-puppet-lint`, is chained to the first and
uses the `puppet-lint` program to check adherence to the Puppet style
guidelines.

Four new unit tests were added to test single line and multiline error
patterns from `puppet-parser`, and to test ERROR and WARNING error
patterns from `puppet-puppet-lint`.

The Vagrant provisioning script has been updated to install puppet.