Higher dimensional reductions

[jw3126]

First of all thanks for this awesome package!

x = randn(3, 3, 4)
@devec m = maximum(x)

Throws the following error:

LoadError: MethodError: `to_length` has no method matching to_length(::Tuple{Int64,Int64,Int64})
while loading In[32], in expression starting on line 5

 in anonymous at ./no file:4294967295

1d and 2d reductions work, as well as 3d stuff like sin(x) + y that does not involve any reductions.