Add some support for historical DST rules

[ddossot]

First: thanks a lot for this much needed library.

It would be great if some support for historical DST rules could be added, as data processing solutions oftentimes have to translate UTC to local time for dates in the past.

For example, in North-America, DST rules changed in 2007 (from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October).

More info: http://en.wikipedia.org/wiki/Daylight_saving_time_around_the_world

Cheers,
David