TEST: move tests for zinc() to the new location.
TEST: move tests for undbv() to the new location.
TEST: move tests for _utils.py to the new location.
TEST: move tests for undbm() to the new location.
TEST: move tests for undbp() to the new location.
TEST: fix import.
TEST: move tests for SIunits() to the new location.
TEST: move tests for rm() to the new location.
Remove deltasigma/test_data.
TEST: move tests for plotPZ() to the new location.
TEST: move tests for plotSpectrum() to the new location.
TEST: move tests for lollipop() to the new location.
TEST: minor changes for consistency.