move from with_<lookup>: to loop:

- old functionality is still available direct lookup use, the following are equivalent

  with_nested: [[1,2,3], ['a','b','c']]

  loop: "{{lookup('nested', [1,2,3], ['a','b','c'])}}"

- avoid squashing with 'loop:'
- fixed test to use new intenal attributes
- removed most of 'lookup docs' as these now reside in the plugins

docs/docsite/rst/playbooks_python_version.rst

@@ -36,9 +36,9 @@ using the :func:`list <jinja2:list>` filter whenever using :meth:`dict.keys`,
       - debug:
           msg: '{{ item }}'
         # Only works with Python 2
-        #with_items: "{{ hosts.keys() }}"
+        #loop: "{{ hosts.keys() }}"
         # Works with both Python 2 and Python 3
-        with_items: "{{ hosts.keys() | list }}"
+        loop: "{{ hosts.keys() | list }}"
 
 .. _pb-py-compat-iteritems:
 
@@ -59,9 +59,9 @@ compatible with both Python2 and Python3::
       - debug:
           msg: '{{ item }}'
         # Only works with Python 2
-        #with_items: "{{ hosts.iteritems() }}"
+        #loop: "{{ hosts.iteritems() }}"
         # Works with both Python 2 and Python 3
-        with_items: "{{ hosts.items() | list }}"
+        loop: "{{ hosts.items() | list }}"
 
 .. seealso::
     * The :ref:`pb-py-compat-dict-views` entry for information on