Add support to getExchangeRate using EUR

Also fix a readme typo

I only tested with my use case. Let me know if you didn't support this on purpose : 

>var settings = {};
>settings.fromCurrency = 'EUR';
>settings.toCurrency = 'CNY';
>currencyConverter.getExchangeRate(settings , function(data){
>     logger.info(JSON.stringify(data));
>     return next(null, data.exchangeRate);
>});