updated hash filters

- added hash_to_tuples filter which can be used to iterate over a hash and
  access as item[0]=>key, item[1]=>value
- added a zipped_hash filter to access multiple lists from a hash in one
  iteration. For example : data = {"a": {"name":"a", "elements" : [1,2,3]}, "b":
  {"name":"b", "elements": [4,5,6]}} =>  with_items: "{{data|zipped_hash('name','elements')}}"
  would result in a list [("a",1),("a",2)....("b",6)].

Some discussion at http://goo.gl/mRB6in & http://goo.gl/p4bn7F suggest
however, that this functionality should be exposed as lookup plugins.
with_hash_items lookup plugin

used to iterate a hash in a task as:
`with_hash_items: ${foo.bar}`. The key and value can be accessed as
item.key & item.value