maxabsfinite is breaking

[johnnychen94]

# in Images
julia> maxabsfinite(rand(RGB, 4, 4))
2.219370615838762

# in ImageBase
julia> maxabsfinite(rand(RGB, 4, 4))
RGB{Float64}(0.9807213248971391,0.9620842090794137,0.9778493728627977)

I also notice that kwargs are not tested.

julia> maxfinite(rand(RGB, 4, 4); dims=1)
ERROR: MethodError: no method matching reducedim_init(::ImageBase.Map12{typeof(isfinite), typeof(identity), typeof(typemin)}, ::typeof(ImageBase.maxc), ::Matrix{RGB{Float64}}, ::Int64)
Closest candidates are:
  reducedim_init(::Any, ::typeof(min), ::AbstractArray, ::Any) at reducedim.jl:129
  reducedim_init(::Any, ::typeof(max), ::AbstractArray, ::Any) at reducedim.jl:129
  reducedim_init(::Any, ::typeof(&), ::Union{Base.AbstractBroadcasted, AbstractArray}, ::Any) at reducedim.jl:159
  ...
Stacktrace:
 [1] _mapreduce_dim(f::ImageBase.Map12{typeof(isfinite), typeof(identity), typeof(typemin)}, op::Function, #unused#::Base._InitialValue, A::Matrix{RGB{Float64}}, dims::Int64)
   @ Base ./reducedim.jl:324
 [2] #mapreduce#672
   @ ./reducedim.jl:310 [inlined]
 [3] maxfinite(A::Matrix{RGB{Float64}}; kwargs::Base.Iterators.Pairs{Symbol, Int64, Tuple{Symbol}, NamedTuple{(:dims,), Tuple{Int64}}})
   @ ImageBase ~/Documents/Julia/ImageBase.jl/src/statistics.jl:34
 [4] top-level scope
   @ REPL[7]:1

Looks like we need more comprehensive tests and compatibility tests for these functions.

[timholy]

Oh that's interesting. I noticed the tests looked a little thin, but I had no idea that I'd changed the implementation.

Do you think we should keep the original scalar-return, or is channelwise better? We have the chance to make a breaking change, of course, and I don't think it's heavily used.

[johnnychen94]

Without considering the compatibility with Images.jl, which I've fixed in JuliaImages/Images.jl@bad872f, I prefer channelwise output as it gives more information on the pixel instead of just the abs value.