Missing generate-id function

[TheKnarf]

The generate-id function generates a unique id for the first node in a given node-set and returns a string containing that id. This function is an XSLT-specific addition to XPath. It is not a part of the core XPath function library. - MDN

• MDN Documentation

• StackOverflow exampe

[berenddeboer]

See #37, at least you get a better error message.

[leonelsanchesdasilva]

#57