Add a parser for the action command language.

Add a parser for the action command language.

The parser generates list of actions (complete with filters).  The parser isn't
called anywhere yet, and uses the incomplete actions_act_new() function.

TODO:
The filters now are just text string key:value pairs. But they should
  become intelligent objects like actions are.
The actions need to change their option parsing from XML to the new key:value
  pair lists.