function index() {
	var out;
	var yr;
	var i;
	out = {};
	for ( i = 0; i < FILES.length; i++ ) {
		yr = FILES[ i ].match( RE )[ 1 ];
		if ( hasOwnProp( out, yr ) ) {
			out[ yr ].push( i );
		} else {
			out[ yr ] = [ i ];
		}
	}
	return out;
}
Generates an index for querying the SOTU database by year.

@private
@returns {Object} database index