title: change currency output of bdh
body: <p>How can I set the currency for this to dollars?</p>
  
  <pre><code>bdh(securities = "SBMAR1 Comdty", fields = 'PX_LAST', start.date = today() - 10, end.date = today())
  </code></pre>
  
  <p>I tried: </p>
  
  <pre><code>bdh(securities = "SBMAR1 Comdty", fields = 'PX_LAST', start.date = today() - 10, end.date = today(), options = c('FX' = 'USD'))
  </code></pre>
  
  <blockquote>
    <p>Error in bdh_Impl(con, securities, fields, start.date, end.date, options,  : 
      Sub-element '(null)' does not exist.</p>
  </blockquote>
  
  <p>and </p>
  
  <pre><code>bdh(securities = "SBMAR1 Comdty", fields = 'PX_LAST', start.date = today() - 10, end.date = today(), options = c('Currency' = 'USD'))
  </code></pre>
  
  <blockquote>
    <p>Error in bdh_Impl(con, securities, fields, start.date, end.date, options,  : 
      Attempt to access unknown sub-element 'Currency' on element 'HistoricalDataRequest'</p>
  </blockquote>