title: Pythonic way to count occurrences from a list in a string
body: <p>What's the best way to find the count of occurrences of strings from a list in a target string? Specifically, I have a list :</p>
  
  <pre><code>string_list = [
      "foo",
      "bar",
      "baz"
  ]
  
  target_string = "foo bar baz bar"
  
  # Trying to write this function!
  count = occurrence_counter(target_string) # should return 4
  </code></pre>
  
  <p>I'd like to optimize to minimize speed and memory usage, if that makes a difference. In terms of size, I would expect that <code>string_list</code> may end up containing several hundred substrings.</p>