Allow arity exceptions on defpartial

[expede]

Should be able to do things like this...

defpartial minus(a, b, c), except: 2, do: a - b - c
defpartial together(a, b, c, d), except: [2,3], do: a <> b <> c <> d

defpartial plus(a, b, c), only: 2, do: a + b + c
defpartial times(a, b, c), only: [1,2], do: a * b * c

...and have it generate or exclude the arities specified.

Once that this the case, we can consider merging Quark.Partial into Quark.Curry, as we won't have the "all arities" problem.