sort: replace Lomuto partitioning with Hoare

I'm seeing numbers aobut the same performance on a
sorted vector of integers, and 21% faster on vector of N
random integers in the range [0, N).
Also, this original algorithm handles well the case
of an array consisting of a repeated value.
The code we are replacing degrates to quadratic time.

* lib.c (med_of_three, middle_pivot): We don't use
the return value, so don't calculate and return one.
(quicksort): Revise to Hoare: scanning from both ends
of the array, exchanging elements.

* tests/010/sort.tl: New file. We test sort with
lists and vectors from length zero to eight, all
permutations.

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