Make symmetric: push/pop which operate on whole items, versus push_bits/pop_bits.  Start adding test infrastructure for push/pop tests.
Make generic fill/drain and lockstep test functions; wire them up for BitBucket tests.
Table/column-alignment formatting change for test definitions.
Remove "edge case tests"; those cases are already exercised by full test vectors; also remove dead test code.
Compare equality by borrowed pointers, not by cloning.