title: Vehicle reloading at depot and continuing
body: <p>I try to generate a delivery plan using ORTOOL and Python.
  My constraints are the following:</p>
  
  <ol>
  <li>Each vehicle has a start time and an end time</li>
  <li>Each vehicle has its own capacity of stored items, taken at the depot</li>
  <li>Each vehicle has its own speed.</li>
  </ol>
  
  <p>For 1 and 3, it works fine using AddDimensionWithVehicleTransits.
  For the second constraint, if the vehicle is empty, it has to return to the depot to retrieve items and start again.</p>
  
  <p>I've seen the refuel example, so setting a node with a capacity &lt; 0 works fine. But in my case, the depot is the refuel point and the solver doesn't make the vehicle return to it.</p>
  
  <p>My dimension is set like that:</p>
  
  <pre><code>routing.AddDimensionWithVehicleCapacity(
      capacity_evaluator,
      0,
      [capacity[vehicle].get('capacity', dataconfig.default_capacity) for vehicle in data.vehicles], 
      True, 
      'Capacity'
  )
  </code></pre>
  
  <p>Basically, with a max capacity of 4:</p>
  
  <pre><code>Route for Vehicle1
  [LOCATION, START, CAPACITY]
  ['Depot', '4:0', 0]
  [u'7', '9:0', 1]
  [u'6', '10:0', 4]
  ['Depot', '11:00', 4]
  </code></pre>
  
  <p>What I need:</p>
  
  <pre><code>Route for Vehicle1
  [LOCATION, START, CAPACITY]
  ['Depot', '4:0', 0]
  [u'Location1', '9:0', 1]
  [u'Location2', '10:0', 4]
  ['Depot', '11:00', 0]
  [u'Location3', '12:0', 1]
  [u'Location4', '13:0', 2]
  [u'Location5', '14:0', 4]
  ['Depot', '15:00', 0]
  </code></pre>
  
  <p>Any idea about how to put the refuel point to the depot ?</p>
  
  <p>Regards</p>