Added capability for supplying default policies for use in other modules

Right now, just a `timeout-policy` is available that the given `body` stops code after a given amount of time (in seconds) if it hasn't finished by then.

Use it like this:
```lisp
(with-policy cpl:timeout-policy (5.0)
  (body-code-goes-here))
```
And for catching the check condition when the timeout actually happens:
```lisp
(with-failure-handling
    ((policy-check-condition-met (f)
      (declare (ignore f))
      (handle-error-here-and-maybe-retry)))
  (with-policy cpl:timeout-policy (5.0)
    (body-code-goes-here)))
```