code: function getId (transaction) {
  	var hash = crypto.createHash('sha256').update(getBytes(transaction).toString('hex'), 'hex').digest();
  	var temp = new Buffer(8);
  	for (var i = 0; i < 8; i++) {
  		temp[i] = hash[7 - i];
  	}
  
  	var id = bignum.fromBuffer(temp).toString();
  	return id;
  }
docs: @method getId
  @param transaction Object
  
  @return {string}