Improve names in nl_NL provider

Improved names in the nl_NL provider (aka Dutch), allowing direct use of `first_name_male` and `first_name_female`; as well as conforming to http://nl.wikipedia.org/wiki/Achternaam#Naamswijziging / http://en.wikipedia.org/wiki/Dutch_name#Dutch_naming_law_.28surnames.29 by adding a "-" between the two last names when someone is married.