r8

• Switch to VapourSynth API V4
• Add an AviSynth+ plugin (API V8 required)
• Add custom kernels (Functionality is about the same as in AkarinVS's fork, but it's implemented in a different way internally) (VapourSynth plugin only)
• Add force/force_h/force_v parameter to force sampling even if the resolution stays the same (VapourSynth plugin only)

Custom kernels usage example:

# Debilinear
core.descale.Descale(src, w, h, custom_kernel=lambda x: 1.0 - x, taps=1)

# Delanczos
import math
def sinc(x):
    return 1.0 if x == 0 else math.sin(x * math.pi) / (x * math.pi)
taps = 3
core.descale.Descale(src, w, h, custom_kernel=lambda x: sinc(x) * sinc(x / taps), taps=taps)