avfilter/hqx: unroll the pattern calculation

Code si smaller, no speed difference.
avfilter/hqx: add some self promotion in doxy.

This is useful to understand how it's different from the original code.
avfilter/avf_showspectrum: fix macro ()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/deshake_opencl: fix macro ()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>