Chronos: Manipulate and format dates, times and intervals

This class can format date and time values and perform several types of manipulation of dates, times and time intervals.

It supports:

- Dates formated in different languages
- Different timezones (conversion & handling)
- Comparison of dates, times and time intervals
- Addition and subtraction of dates with time intervals
- Some special "goto" methods to quickly get a given week of the year or month, or a given day of the year, week or month
- Output formatted dates, times and time intervals in several ways: human readable, UNIX time, MySQL formatted,...
- Calculate date values for specific purposes: get the Zodiac sign, compute the age, ...
- It is not restricted by Unix-like system specific limitations of handling dates between 1970 and 2038
- Retrieving fractions of dates, times and time intervals, like for instance how many months are in a given interval, which day of the year is a given day, ...