rasterize method is too restrictive on argument types

[gszep]

the current type signature uses Matrix{Float64} for points and colors positional arguments which is too restrictive and does not allow for useful color formats such as ::Array{Normed{UInt8,8},2} or views into larger arrays such as ::SubArray. Would recommend using AbstractMatrix{<:Number} instead

[exaexa]

Will have a look at it. Certainly I guess we can go at least with AbstractMatrix{AbstractFloat}.

[gszep]

in fact it seems that rasterize is current doing a lot of conversion from Float64 to Int64 which we can avoid by having additional method where colors::AbstractMatrix{Normed{UInt8,8}}

[gszep]

you can also consider handling colors::AbstractVector{<:Colorant} from https://github.com/JuliaGraphics/ColorTypes.jl

[gszep]

Note that Normed{UInt8,8} is not an AbstractFloat so you would need a more general abtract type to capture it