Port all methods (except task creation) to free functions

[richfitz]

Lots of churn here!

I've copied over all implementations into the free function versions; sometimes these were a bit scattered around. Docs are duplicated between the controller and the main version, which adds to the sense of duplication too.

One line of the tests change, everything else retains the same interface.

Next step after this is to add versions of the task creation functions (replacing our current enqueue, enqueue_ etc) which will not be backward compatible, then porting hint

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (042b6fd) 99.65% compared to head (dd37da7) 99.68%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #104 +/- ## ========================================== + Coverage 99.65% 99.68% +0.02% ========================================== Files 30 33 +3 Lines 2040 2211 +171 ========================================== + Hits 2033 2204 +171 Misses 7 7 ```

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