title: Find all combinations of a set of numbers that add up to a certain total
body: <p>I've seen a few solutions to similar problems, but they all require iteration over the number of items to be added together.</p>
  
  <p>Here's my goal: from a list of numbers, find all of the combinations (without replacement) that add up to a certain total. For example, if I have numbers <code>1,1,2,3,5</code> and total <code>5</code>, it should return <code>5</code>,<code>2,3</code>, and <code>1,1,3</code>.</p>
  
  <p>I was trying to use <code>combn</code> but it required you to specify the number of items in each combination. Is there a way to do it that allows for solution sets of any size?</p>