Alternative ways to handle days overflowing months

[ariebovenberg]

Handling the common "too many days in a month" situation should be customizable.

For example Date(2017, 1, 30).add(month=1) currently truncates the result: Date(2017, 2, 28). While this is what many libraries do by default, it may be worth adding different options, like (1) extrapolating ("roll over") or (2) raising an exception.

Places where this could be useful:

• adding/subtracting months/years
• (?) replacing the day/month component of a date(time)
• (?) constructing dates and datetimes