Add Country#alpha2 and update DSL

Modify the Country object to hold an alpha2 field, and update the DSL
to include a require include a new value immediately following the
country_code.
Create a new NanpCountryDetector

Used for detecting where multiple countries use the same prefix. In
this case, this covers NANP (based upon the Wikipedia article on NANP).
Modify all country definitions to use new DSL

All Alpha2 codes drawn from Wikipedia.
Phony & CountryCodes extensions

Add #country and #recognized_countries methods to Phony and
CountryCodes. #country detects the Alpha2 of number of the guessed
country, while #recognized_countries returns an array of all recognised
countries. Includes specs.