Consumes content inside round braces. Mostly used to skip `;` token inside
expressions since in LESS it is also used to separate function arguments
@param  {StringReader} stream
@param  {Stylesheet}   root   A stylesheet root. Used to accumulate comments
@return {Boolean}
function eatBraces(stream, root) {
	if (stream.eat(LBRACE)) {
		let stack = 1, token;

		while (!stream.eof()) {
			if (stream.eat(RBRACE)) {
				stack--;
				if (!stack) {
					break;
				}
			} else if (stream.eat(LBRACE)) {
				stack++;
			} else if (eatUrl(stream) || eatString(stream)) {
				continue;
			} else if (token = comment(stream)) {
				root.addComment(token);
				continue;
			} else {
				stream.next();
			}
		}

		return true;
	}

	return false;
}