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

- String: test cases for numerical conversion
- String: Implement String != regex operator
- String: index and rindex methods with String argument
- String: format operator % like in python
- String: split and join
- String: assign fstream objects to read and write a file
- regex:  throw an exception when contructing a regex returns an error

- 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 time_t, struct tm

- Add classes: xml, configuration, amount