Things to do or consider

Add an additional constructor that accepts a single TimeChangeRule, for locales that do not observe DST.

Add notes in ReadMe.txt: EEPROM addresses are not checked/validated, there must be 2x12 bytes available at the given address when using Timezone::writeRules(int address).

Investigate possible efficiencies by storing _dst.offset * SECS_PER_MIN and _std.offset * SECS_PER_MIN as private members. Possible trade off between library size and avoiding multiplications in several places.