v0.4.1

• ISO: Fixed symbols for BHD, ISK, NPR, UYU and alpha code for UYW.
• ISO: Added ALL, STN, UYW currencies @ObsceneGiraffe.
• Crypto: Added COMP, DAI, MKR, UNI, USDC, USDT, XTZ, ZEC
• Fix: Exchange::get_rate returns a lifetime Option<ExchangeRate<'a, T>> to prevent lifetime conflicts @RestitutorOrbis.