RFC: Continuous Integration With Travis CI

## Background

We've been making a few changes to this module recently and I want to ensure that it meets the same high standards as we expect of Envato production code.

## Changes

- Grab sample Gem and Rake files from https://github.com/garethr/puppet-module-skeleton/
- Fix obvious `puppet-lint` violations
- [Write a metadata.json File](https://docs.puppetlabs.com/puppet/latest/reference/modules_publishing.html#write-a-metadatajson-file)
- Tweak `rake` to run all the tests (such as they are) by default
- Modify `.travis.yml` to provide more information when a build fails
- Refine `Gemfile` so that builds pass with many Rubies and Puppets.
- Upgrade README to [GFM](https://help.github.com/articles/github-flavored-markdown/), with embedded Build Status indicator.

## TODO

```sh
% bundle exec rspec
No examples found.

Finished in 0.00006 seconds
0 examples, 0 failures
```

:disappointed: 

Cc: @envato/d-e-r-p