function simplify(folds) {
        if (!folds) {
            return;
        }
        var res = {}, range;
        Object.keys(folds).forEach(function (line) {
            range = folds[line];
            res[line] = Array.isArray(range) ? range : [[range.from.line, range.from.ch], [range.to.line, range.to.ch]];
        });
        return res;
    }
Simplifies the fold ranges into an array of pairs of numbers.
@param {!Object} folds the raw fold ranges indexed by line numbers
@return {Object} an object whose keys are line numbers and the values are array
of two 2-element arrays. First array contains [from.line, from.ch] and the second contains [to.line, to.ch]