Adding Tests

Hi @sarahs 

This pull request adds a single test to the repo, and we can expand on these as we go. I like writing tests for this kind of stuff, so we can make sure the templates perform like we want them to. To run the tests, first install the dependencies:

```ruby
$ bundle install
```

Then run the tests:

```ruby
$ rake spec
```

I made a function called `convert` that runs the asciidoc -> HTMLBook converter. I then use Nokogiri to parse the html output and check that the nodes have the correct value. This is basically the way we would write these tests.

If this looks good to you, feel free to merge in.