Things to do:
=============

- String: format operator % like in python
- String: assign fstream objects to read and write a file
- String: convert to and from std::sstream

- SuperString: sort and uniq
- SuperString: find (regex)
- SuperString: remove empty elements or elements macthing a pattern

- date: test parser for invalid dates and syntax errors
- date: Parser for stream input
- date: Yearday, Weekday and week number

- UTC: Convert to and from  struct tm

- xml: Xinclude processing

- configuraion: Handle environment variables to override parameters