Ruslan Mardugalliamov

@harshjk your code does not pass the maven checks. Looks like the code misses the mandatory license header. Could you please address it first? Additionally, could you attach the test...

> Taking a deeper dive, Would be great if you could also update developer guide for functions - [link](https://github.com/prestodb/presto/blob/master/presto-docs/src/main/sphinx/develop/functions.rst) Added documentation.