Adds the [currency] and [currency_legal] shortcodes to convert currencies based on the ECB reference exchange rates.
The European Central Bank (ECB) daily publishes "foreign exchange reference rates" against more than 30 other currencies. These rates are used by this plugin.
The rates are published for informational purposes only and exchange rates may vary.
See http://www.ecb.europa.eu/stats/eurofxref/ for more information.