divide/list returns empty list for pure hash tables with one entry

[DalekBaldwin]

divide returns nil as the first value and the hash table's single entry as the second value, but it looks like divide/list assumes the opposite: https://github.com/fare/lisp-interface-library/blob/master/pure/hash-table-implementation.lisp#L128-L129

Test to demonstrate:
DalekBaldwin@de1d566

[fare]

Oops. Can you send me a patch, including adding a regression test to the test suite?

[DalekBaldwin]

I'm not familiar enough with the internals to be confident fixing it by myself. It looks like this would work:

(defmethod divide/list ((i <hash-table>) map)
  (let ((list (divide/list (hashmap-interface i) map)))
    (if (cdr list)
        list
        (multiple-value-bind (a b) (divide i map)
          (declare (ignore a))
          (if (empty-p (hashmap-interface i) b)
              nil
              (list b))))))

But I don't know for certain if the nil value will always be the first value, or if there are rare cases where this won't work.

[fare]

ignoring a is obviously wrong. I reimplemented that method to use divide/list on the bucketmap where appropriate.

I added better tests for divide and divide/list, and also found and fixed issues with dividing trie's.
Finally, I improved the docstring for divide.