Revert "Revert "Get rid of fftw dependency""

This reverts commit 8fccc13312eac6a3d1e0dbb0aae92d132035443a.

In other words, get rid of fftw again.
Revert "readme.rst: dct parameter is back"

This reverts commit 06f6f6af75a37a2c2c8b684681af9023d04d6d4b.
readme.rst: New reason for removing "dct"
Add SimpleResize, required by the next two filters
readme.rst: There is no "planar" parameter anywhere
Add Mask
Add Finest

Required by FlowBlur.
Add FlowBlur
Sanity checking for more parameters