Add support for various historic/non-ISO currency codes

[salimshopbou]

While debugging this issue I found a few currency codes that are coming back invalid that may be worth adding support for.

RMB - non ISO currency code for the Chinese Yuan (CNY).
VEB - Old Venezuelan Bolivar. An entry for this actually exists in the yml configs but it doesn't seem to work when calling Money::Helpers.value_to_currency
TVD - Tuvaluan Dollar