code: function getLevelFromToken(token) {
    // leaf level token size is 16. Each 2 bit add a level
    const lastHex = token.substr(token.length - 1);
    // a) token = trailing-zero trimmed hex id
    // b) 64 bit hex id - 3 face bit + 60 bits for 30 levels + 1 bit lsb marker
    const level = 2 * (token.length - 1) - ((lastHex & 1) === 0);
    // c) If lsb bit of last hex digit is zero, we have one more level less of
    return level;
  }
docs: Given a S2 hex token this function returns cell level
  cells level is a number between 1 and 30
  
  S2 cell id is a 64 bit number
  S2 token removed all trailing zeros from the 16 bit converted number