function onFiles( error, files ) {
		var idx;
		if ( error ) {
			debug( 'Encountered an error when reading README file contents. Error: %s', error.message );
			return done( error );
		}
		debug( 'Creating search index.' );
		idx = createIndex( files );
		debug( 'Successfully created search index.' );
		done( null, idx );
	}
Callback invoked after retrieving file contents.

@private
@param {(Error|null)} error - error object
@param {ObjectArray} files - list of files and their contents
@returns {void}