Add parsing of snailmail addresses, for GMail and Yahoo

This pull request adds snailmail address components (address_1, address_2, city, region, and postcode) to the pieces OmniContacts will parse upon retrieving contacts from GMail or Yahoo (but not Facebook or Hotmail).  Region is intended to be the state, province, or whatever else the country may be divided into at a top level.  Postcode is zip code or non-US equivalent.  It does NOT currently parse the country -- I was doing this on a client's dime and he didn't need that, but someone could easily add it later.

It also:

- adds tests for this functionality,
- makes a chunk of code I had to modify anyway a bit more Ruby-idiomatic and efficient,
- updates the README a bit, and
- turns the feature/provider table sideways, so that more features can be added to it without running out of room.  :-)