Auto-generate specialized scalers for taps = [2-12]

benchmark                   old MB/s     new MB/s  speedup
BenchmarkBilinearUp           125.26       194.27    1.55x
BenchmarkBilinearUp-2         225.38       365.91    1.62x
BenchmarkBilinearUp-4         430.42       654.78    1.52x
BenchmarkBicubicUp             92.51       121.83    1.32x
BenchmarkBicubicUp-2          163.52       212.74    1.30x
BenchmarkBicubicUp-4          319.16       415.58    1.30x
BenchmarkLanczosUp             72.63        94.65    1.30x
BenchmarkLanczosUp-2          133.49       167.94    1.26x
BenchmarkLanczosUp-4          249.82       298.20    1.19x
BenchmarkBilinearDown          24.84        33.54    1.35x
BenchmarkBilinearDown-2        47.31        63.96    1.35x
BenchmarkBilinearDown-4        83.78       108.01    1.29x
BenchmarkBicubicDown           16.44        21.12    1.28x
BenchmarkBicubicDown-2         31.73        40.35    1.27x
BenchmarkBicubicDown-4         55.99        69.62    1.24x
BenchmarkLanczosDown           12.22        12.71    1.04x
BenchmarkLanczosDown-2         23.38        24.15    1.03x
BenchmarkLanczosDown-4         40.99        42.78    1.04x
BenchmarkBicubicIUp            92.02       121.21    1.32x
BenchmarkBicubicIUp-2         167.94       218.72    1.30x
BenchmarkBicubicIUp-4         315.92       410.86    1.30x
BenchmarkBicubicIDown          91.64       120.79    1.32x
BenchmarkBicubicIDown-2       166.50       214.35    1.29x
BenchmarkBicubicIDown-4       312.90       413.04    1.32x