title: Count number of including weeks between 2 dates
body: <p>I need to get the number of weeks between 2 dates.<br>
  A week for me is monday to sunday.<br>
  So if the first date is on a saturday than this week should be included.<br>
  if the second date is on a monday than this week should be included.</p>
  
  <p>What is the most efficient way to do this ?</p>
  
  <p>example :  </p>
  
  <pre><code>startdate   enddate      nbr of weeks
  17/09/2016  26/09/2016   3 weeks
  17/09/2016  25/09/2016   2 weeks
  19/09/2016  26/09/2016   2 weeks
  12/09/2016  25/09/2016   2 weeks
  </code></pre>
  
  <p>I found much answers for this, like this one for example <a href="https://stackoverflow.com/questions/4604199/how-to-calculate-number-of-weeks-given-2-dates">how to calculate number of weeks given 2 dates?</a> but they all end up with dividing the days with 7 and that does not gives the result I need.</p>