Adding Gaussian Pyramid

After I couldn't find a gaussian pyramid implementation in Julia I quickly made a simple implementation:

struct Pyramid{T,M<:AbstractMatrix{T}} <: AbstractMatrix{T}
    data::Vector{M}
end

function Pyramid(data::AbstractMatrix; min_resolution=1024, mode=Linear())
    ranges(d) = (LinRange(1, size(data, 1), size(d, 1)), LinRange(1, size(data, 2), size(d, 2)))
    ET = ImageBase.restrict_eltype(first(data))
    resized = convert(Matrix{ET}, data)
    pyramid = [interpolate(eltype(ET), ET, ranges(resized), resized, Gridded(mode))]
    while any(x -> x > min_resolution, size(resized))
        resized = restrict(resized)
        interp = interpolate(eltype(ET), ET, ranges(resized), resized, Gridded(mode))
        push!(pyramid, interp)
    end
    Pyramid(pyramid)
end

function (p::Pyramid)(x::LinRange, y::LinRange)
    xystep = step.((x, y))
    maxsize = size(p.data[1])
    val, idx = findmin(p.data) do data 
        steps = step.(LinRange.(1, maxsize, size(data)))
        norm(xystep .- steps)
    end
    level = p.data[idx]
    return level(x, y)
end

function Base.size(p::Pyramid)
    return size(p.data[1])
end
function Base.show(io::IO, ::MIME"text/plain", p::Pyramid)
    show(io, p)
end
function Base.show(io::IO, p::Pyramid)
    println(io, "Pyramid with levels: $(size.(p.data))")
end

Is this something we want to add to ImageBase?

Review the proposed Pyramid implementation and the ImageBase APIs it uses, especially restrict and interpolate. The issue names no target file or tests; if accepted, done should include an agreed API and verified pyramid construction, level selection, sizing, and display behavior.