title: Merge and sum of two dictionaries
body: <p>I have a dictionary below, and I want to add to another dictionary with not necessarily distinct elements and merge it's results. Is there any built-in function for this, or will I need to make my own?</p>
  
  <pre><code>{
    '6d6e7bf221ae24e07ab90bba4452267b05db7824cd3fd1ea94b2c9a8': 6,
    '7c4a462a6ed4a3070b6d78d97c90ac230330603d24a58cafa79caf42': 7,
    '9c37bdc9f4750dd7ee2b558d6c06400c921f4d74aabd02ed5b4ddb38': 9,
    'd3abb28d5776aef6b728920b5d7ff86fa3a71521a06538d2ad59375a': 15,
    '2ca9e1f9cbcd76a5ce1772f9b59995fd32cbcffa8a3b01b5c9c8afc2': 11
  }
  </code></pre>
  
  <p>The number of elements in the dictionary is also unknown.</p>
  
  <p>Where the merge considers two identical keys, the values of these keys should be summed instead of overwritten.</p>