Add a (failing) unit test for the new (not yet implemented) get_abs_max
and get_abs_min methods on the BucketResampler class.

First attempt to implement get_abs_max for the bucket resampler.  It's
failing because ``da.where`` return ``NotImplemented``.  I don't
understand the problem.

Fix the implementation for get_abs_max.

Remove implementation and test for get_abs_min because it's harder to
implement and I don't need it.

Remove some code that is unreachable and untested

Recover the unit test accidentally deleted in a previous commit.

If I increase max_computes in the unit test, the test passes

rename min/max local variables as to not shadow builtins

Change max-computes from 3 to 0 in get_abs_max test

In the bucket resampler get_abs_max method, add the missing fill_value
to the method documentation.

Refactor the BucketResampler.get_abs_max method.  Move the calculation
of the abs_max from min and max to its own (pseudoprivate) method.