Update dehalo_alpha

[Setsugennoao]

From Zewia:

• [x] what do you think about adding an iterations parameter to dehalo_alpha

i find that applying the filter multiple times at weaker strengths is usually better than one call at a strong strength

[LightArrowsEXE]

I'd also like to see a List[float] for rx/ry so we can determine strength on a per-plane basis. Right now we need to call the function twice, once with planes=0 and once with planes=[1, 2].

[Setsugennoao]

Added both suggestions. Zewia's: https://github.com/Irrational-Encoding-Wizardry/vs-dehalo/commit/97f8dd708c5ea546ab9b4c71b8529a57278d2f05, Light's: https://github.com/Irrational-Encoding-Wizardry/vs-dehalo/commit/f262402823c85b4f0cf21d499eebfc6129a760fe.