Add support for a supplemental `chef-client` attributes file in YAML and a configuration-by-convention directory structure
Add the `OsX::Bootstrap::Formatter` class for framed, line-wrapped messages
Add some informative terminal output for guiding the user through the installation process
Add support for recursively traversing a directory of `_attributes.yml` files and merging them into one
Update the default rbenv Ruby version to `2.1.4`
Update the installer so that it responds properly to changes in the default rbenv Ruby version
Generate the `osx-bootstrap` wrapper script for caching the installer's command-line arguments