Merge changes from hooke.util.fft

Merge changes from hooke.util.fft

I'd bundled FFT_tools into Hooke back in 2010, when I was optimistic
about getting my Hooke branch accepted upstream.  Now that that seems
less likely, I'm went to tear the module back out of Hooke, and I
noticed some useful restructuring.  Here it is, merged back into the
FFT-tools.

Changes:

* Fancy Sphinx/numpydoc-style docstrings
* unittest-based test suite.

Conflicts:
  FFT_tools.py

The bulk of the conflics were due to parallel style cleanups, and had
trivial fixes.  I also copied the test code relatively unchanged from
the FFT-tools branch into the Hooke unittest framework.  Here is the
mapping:

Old FFT-tools function                       New unittest method
-------------------------------------------  ---------------------------------------------------------------
_test_rfft                                   TestRFFT.run_rfft
_test_rfft_suite                             TestRFFT.test_rfft
_test_unitary_rfft_parsevals                 TestUnitaryRFFT.run_unitary_rfft_parsevals
_test_unitary_rfft_parsevals_suite           TestUnitaryRFFT.test_unitary_rfft_parsevals
_rect                                        TestUnitaryRFFT.rect
_test_unitary_rfft_rect                      TestUnitaryRFFT.run_unitary_rfft_rect
_test_unitary_rfft_rect_suite                TestUnitaryRFFT.test_unitary_rfft_rect
_gaussian                                    TestUnitaryRFFT.gaussian
_test_unitary_rfft_gaussian                  TestUnitaryRFFT.run_unitary_rfft_gaussian
_test_unitary_power_spectrum_sin             TestUnitaryPowerSpectrum.run_unitary_power_spectrum_sin
_test_unitary_power_spectrum_sin_suite       TestUnitaryPowerSpectrum.test_unitary_power_spectrum_sin
_test_unitary_power_spectrum_delta           TestUnitaryPowerSpectrum.run_unitary_power_spectrum_delta
_test_unitary_power_spectrum_delta_suite     TestUnitaryPowerSpectrum.test_unitary_power_spectrum_delta
_gaussian2                                   TestUnitaryPowerSpectrum.gaussian
_test_unitary_power_spectrum_gaussian        TestUnitaryPowerSpectrum.run_unitary_power_spectrum_gaussian
_test_unitary_power_spectrum_gaussian_suite  TestUnitaryPowerSpectrum.test_unitary_power_spectrum_gaussian
_test_unitary_avg_power_spectrum_sin         TestUnitaryAvgPowerSpectrum.run_unitary_avg_power_spectrum_sin
_test_unitary_avg_power_spectrum_sin_suite   TestUnitaryAvgPowerSpectrum.test_unitary_avg_power_spectrum_sin