title: subset xts object out of a time period
body: <p>I have got a large xts object containing quite a lot observations. I know that it is possible to get the data in certain time periods using x["yyyy-mm-dd/yyyy-mm-dd", "yyyy-mm-dd/yyyy-mm-dd", "yyyy-mm-dd/yyyy-mm-dd"]. But how can I delete the data in those time periods and get the rest?</p>
  
  <p>Many thanks in advance!</p>