Implementation of poly2mask from matlab

Hi,

I was looking for implementation of a function, which would fill an image region based on the provided polygon. It exists in Matlab (poly2mask) and also was re-implemented in python (see the discussion).

The implementation is almost trivial (see below), and the function seems generally useful. Would you be interested in me making a PR?

function point_in_polygon(poly_xs::Vector{T}, poly_ys::Vector{T}, x::T, y::T) where T<: Real
    n_verts = length(poly_xs)
    j = n_verts
    c = false
    for i in 1:n_verts
        if (((poly_ys[i] <= y) && (y < poly_ys[j])) || ((poly_ys[j] <= y) && (y < poly_ys[i]))) && 
            (x < (poly_xs[j] - poly_xs[i]) * (y - poly_ys[i]) / (poly_ys[j] - poly_ys[i]) + poly_xs[i])
            c = !c
        end
        j = i
    end
    return c
end

function draw_polygon!(mask::Matrix{T2}, poly_xs::Vector{T}, poly_ys::Vector{T}, value::T2) where T<: Integer where T2 <: Real
    min_x, max_x = max(minimum(poly_xs), 1), min(maximum(poly_xs), size(mask, 2))
    min_y, max_y = max(minimum(poly_ys), 1), min(maximum(poly_ys), size(mask, 1))
    for y in min_y:max_y
        for x in min_x:max_x
            if point_in_polygon(poly_xs, poly_ys, x, y)
                mask[y, x] = value
            end
        end
    end
end

function polygons_to_mask(polygons::Array{Matrix{T}, 1} where T <: Real, max_x::Int, max_y::Int)
    poly_mask = zeros(Int, max_y, max_x);
    for (i,p) in enumerate(polygons)
        draw_polygon!(poly_mask, round.(Int, p[:,1]), round.(Int, p[:,2]), i)
    end
    return poly_mask
end

Start with the issue's MATLAB poly2mask reference and the supplied Julia point_in_polygon, draw_polygon!, and polygons_to_mask examples. Confirm the desired polygon and mask behavior, then add coverage showing that polygon regions are converted into the expected mask values.