title: MooTools: Get the first and last days of a given week
body: <p>I'm relatively inexperienced in JavaScript (we're using MooTools, here) and I'm stuck with a problem:</p>
  
  <p>Is there a quick way to get the first and last dates of a given week? 
  e.g. week 17 / 2015 starts on Monday, April 20th and ends on Sunday, April 26th.</p>
  
  <p>My goal is to find out if a given week starts and ends in the same month (week 18 wont, since it starts on April 27th and ends on May 3rd).</p>
  
  <p>Many thanks on any help with examples or pointing me to the right documentation. 
  I've been looking for a while and haven't found anything like this, and I find MooTools documentation very poor...</p>