Use the UK's HMRC Currency conversion rates for VAT as a source of currency conversion

Hi, this is a fantastic project - it would be great if it pulled from this source: 

https://www.trade-tariff.service.gov.uk/exchange_rates/monthly

Which would give it a complete set of currencies. The ECB seems to only have a small cherry picked list!

The formats are all in CSV so should be easy to implement.

Keep up the good work!