4 - String: test cases for numerical conversion
5 - String: Implement String != regex operator
6 - String: index and rindex methods with String argument
7 - String: format operator % like in python
8 - String: split and join
9 - String: assign fstream objects to read and write a file
11 - date: test parser for invalid dates and syntax errors
12 - date: Parser for stream input
13 - date: Yearday, Weekday and week number
15 - UTC: Convert to and from time_t, struct tm
17 - Add classes: xml, configuration, amount