Add a split filter.

Often it is convenient to pass an argument on the command line that could be used as an iterable.  This patch provides a 'split' filter which mimics the python str.split interface.

An example playbook using it:

    ---
    - hosts: localhost
      tasks:
        - debug: msg="{{ item }}"
          with_items: "{{ foo|split(sep=',') }}"

Executing it:

    $ ansible-playbook test.yml -e "foo=1,2,3"

    PLAY [localhost] ************************************************************** 
    
    GATHERING FACTS *************************************************************** 
    ok: [localhost]
    
    TASK: [debug msg="{{item}}"] ************************************************** 
    ok: [localhost] => (item=1) => {"item": "1", "msg": "1"}
    ok: [localhost] => (item=2) => {"item": "2", "msg": "2"}
    ok: [localhost] => (item=3) => {"item": "3", "msg": "3"}
    
    PLAY RECAP ******************************************************************** 
    localhost                  : ok=2    changed=0    unreachable=0    failed=0