Add a lot more information to the README
Handle errors for empty radioset and checkboxset inputs

Previously, this raised an exception as it assumed there was at
least one input.  This handles the case where there are no inputs,
by just putting in the error message span.
Prefer name and id to key for radioset/checkboxset inputs

This is for consistency with all of the other inputs.
Make explicit labeler handle :key and :key_id options
Merge remote branch 'upstream/master'
Suggested modifications to Readme.rdoc