function filterFiles( list ) {
	var out;
	var ext;
	var i;

	out = [];
	for ( i = 0; i < list.length; i++ ) {
		ext = extname( list[ i ] );
		if ( ext === '.txt' ) {
			out.push( list[ i ] );
		}
	}
	return out;
}
Filters a list of files for documentation files.

@private
@param {Array} list - file list
@returns {Array} filtered list