Add default R package files
Add script which will contain the package functions. Add function download_public_data() to script.
Update basic R package documentation given the addition of the download_public_data()  function.
Change the file argument to db_file so that it is clear that the file must be a database file. This option only makes sense for sqlite and msaccess connections.
Update help file for the download_public_data() function given the change to the file argument.
Add install and example instructions to README.md
Replace the function download_public_data() with install_data(). Also add functions for updating scripts, creating an new script, and for listing the available datasets.
Replace the helpfile for download_public_data with a help file for the function install_data()
Add help files for functions data_ls(), new_script(), and update_scripts().
Merge pull request #2 from dmcglinn/master

Create the skeleton of an R package with a basic Retriever interface