Fix debugging relic that resulted in significant inefficiency in real-space convolution
(#439)
Fix some odd low-level artifacts in FFT by setting k=N/2 values explicitly to 0.
(#439)
Update test_offset to include non-integer offsets.
(#439)
Revert "Fix some odd low-level artifacts in FFT by setting k=N/2 values explicitly to 0."

This reverts commit f26534e67f203b9c9b96c6c030deb2635638ddab.
Only expect 5 digits of accuracy on centroid due to finite image size and such.
(#439)