Adding exceptional and transitional reservations.

[amckenna41]

Adding exceptional and transitional ISO 3166-1 alpha-2 code allocations. These may be lesser known and used states/jurisdictions/bodies but are still good to include as they are technically still part of the ISO3166 standard. Putting the list of additions below:

• Ascension Island - AC (exceptional)
• Burma - BU (transitional)
• European Union - EU (exceptional)
• Eurozone - EZ (exceptional)
• French, metropolitan - FX (exceptional)
• Island of Sark - CQ (exceptional)
• Netherlands Antilles - AN (transitional)
• Neutral Zone - NT (transitional)
• Tristan da Cunha - TA (exceptional)
• United Nations - UN (exceptional)
• USSR - SU (exceptional)
• Yugoslavia - YU (transitional)
• Zaire - ZR (transitional)

Reference: https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#Exceptional_reservations