Allow a user to exclude certain JavaScript files

Allows a user to configure hound to ignore specified JavaScript files
from being run through the jshint through an "exclude" configuration.

Example configuration:

```yaml
java_script:
  enabled: true
  exclude:
    - "app/assets/javascripts/*.js"
```
The jshint file is similar to a gitignore file, so they aren't indented. Just separated by a new line.