title: Use character string as function argument
body: <p>I'm sure this is simple, but I cannot find a solution ...
  I would like to use a variable containing a character string as argument for a function.</p>
  
  <pre><code>x &lt;- c(1:10)
  myoptions &lt;- "trim=0, na.rm=FALSE"
  </code></pre>
  
  <p>Now, something like</p>
  
  <pre><code>foo &lt;- mean(x, myoptions)
  </code></pre>
  
  <p>should be the same as</p>
  
  <pre><code>foo &lt;- mean(x, trim=0, na.rm=FALSE)
  </code></pre>
  
  <p>Thanks in advance!</p>