Extend lists of currencies and the Currency interface

List of currencies that should be supported:

Updates to currency lists:

[ ] Check and update ISO 4217 symbols and short symbols.
[ ] Use go gen to retrieve list of currencies and their symbols and other information if possible.

Useful fields that should be added to the Currency interface:

[ ] Replaced by currency.
[ ] Rate of exchange with the replacement currency.
[ ] Time range when the currency was official.
[ ] Formatting template. Not sure how to do it, as it is also locale dependent.
[ ] Plural and singular variants for symbols. Complex problem as that also depends on the locale and currency. There may be exceptions for zero values, negative values...
[x] Replace DecimalPlaces with SmallestUnit that returns the value of the smallest unit. Add helper function to get decimal places to fully represent that decimal unit.
[x] Add numeric code

Dadido3 / D3money