code: public static <T> Collection<T> leftShift(Collection<T> self, T value) {
          self.add(value);
          return self;
      }
docs: Overloads the left shift operator to provide an easy way to append
  objects to a Collection.
  <pre class="groovyTestCase">def list = [1,2]
  list &lt;&lt; 3
  assert list == [1,2,3]</pre>
  
  @param self  a Collection
  @param value an Object to be added to the collection.
  @return same collection, after the value was added to it.
  @since 1.0