ISO 4217 currency codes

This crate provides an enum that represents all ISO 4217 currencies and has simple methods to convert between numeric and character code, list of territories where each currency is used, and the English name of the currency.

The data for this is taken from https://en.wikipedia.org/wiki/ISO_4217

Examples

```rust use iso_currency::Currency;

asserteq!(Currency::EUR.name(), "Euro"); asserteq!(Currency::EUR.numeric(), 978); asserteq!(Currency::fromnumeric(978), Some(Currency::EUR)); asserteq!(Currency::fromcode("EUR"), Some(Currency::EUR)); asserteq!(Currency::CHF.usedby(), vec!["Liechtenstein", "Switzerland"]); assert_eq!(format!("{}", Currency::EUR.symbol()), "€"); ```