How do I get exchange rates by date?
<p>I am interested to find exchange rates by a certain date. Do you guys know what API I can use for this? (Preferably, a free API.)</p>

<p>I create an object with creation date the <em>20th of May, 2016</em>. That object has a price in EUR. I want to be able to get the exchange rate of EUR to USD for that date and convert it to USD. </p>