Barplot enhancement

[piever]

From here, it seems that barplot also accepts x 1 element longer than y, in which case, it's used as "edges" rather than "centers", but it currently errors in two different places:

julia> barplot([1, 5, 6, 10], [1,2,3])
ERROR: DimensionMismatch("arrays could not be broadcast to a common size")
Stacktrace:
 [1] _bcs1 at ./broadcast.jl:439 [inlined]
 [2] _bcs at ./broadcast.jl:433 [inlined]
 [3] broadcast_shape at ./broadcast.jl:427 [inlined]
 [4] combine_axes at ./broadcast.jl:422 [inlined]
 [5] instantiate at ./broadcast.jl:266 [inlined]
 [6] materialize(::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1},Nothing,typeof(+),Tuple{Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1},Nothing,typeof(last),Tuple{Array{Vec{2,Float32},1}}},Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{1},Nothing,typeof(last),Tuple{Array{Point{2,Float32},1}}}}}) at ./broadcast.jl:724
 [7] data_limits(::BarPlot{...}) at /home/pietro/.julia/dev/AbstractPlotting/src/basic_recipes/basic_recipes.jl:457
 [8] macro expansion at /home/pietro/.julia/dev/AbstractPlotting/src/basic_recipes/basic_recipes.jl:356 [inlined]
 [9] macro expansion at /home/pietro/.julia/dev/AbstractPlotting/src/utilities/logging.jl:79 [inlined]
 [10] macro expansion at /home/pietro/.julia/dev/AbstractPlotting/src/utilities/logging.jl:15 [inlined]
 [11] (::getfield(AbstractPlotting, Symbol("##500#504")){Scene,BarPlot{...}})(::AbstractPlotting.Automatic, ::Vec{3,Float32}) at /home/pietro/.julia/dev/AbstractPlotting/src/basic_recipes/basic_recipes.jl:346
 [12] map_once(::Function, ::Reactive.Signal{Any}, ::Reactive.Signal{Any}) at /home/pietro/.julia/dev/AbstractPlotting/src/interaction/nodes.jl:80
 [13] plot!(::Scene, ::BarPlot{...}, ::Attributes) at /home/pietro/.julia/dev/AbstractPlotting/src/basic_recipes/basic_recipes.jl:344
 [14] plot!(::Scene, ::Type{BarPlot{...}}, ::Attributes, ::Array{Int64,1}, ::Vararg{Array{Int64,1},N} where N) at /home/pietro/.julia/dev/AbstractPlotting/src/interfaces.jl:392
 [15] #plot!#155 at /home/pietro/.julia/dev/AbstractPlotting/src/interfaces.jl:369 [inlined]
 [16] plot! at /home/pietro/.julia/dev/AbstractPlotting/src/interfaces.jl:369 [inlined]
 [17] #plot#149 at /home/pietro/.julia/dev/AbstractPlotting/src/interfaces.jl:356 [inlined]
 [18] plot at /home/pietro/.julia/dev/AbstractPlotting/src/interfaces.jl:356 [inlined]
 [19] #barplot#310 at /home/pietro/.julia/dev/AbstractPlotting/src/recipes.jl:77 [inlined]
 [20] barplot(::Array{Int64,1}, ::Array{Int64,1}) at /home/pietro/.julia/dev/AbstractPlotting/src/recipes.jl:77
 [21] top-level scope at none:0

julia> barplot([1, 5, 6, 10], [1,2,3], raw = true)
Error showing value of type Scene:
ERROR: buffer scale has not the same length as the other buffers.
              Has: 3. Should have: 4

I also believe that if the user passes edges, widths should correspond to the edges, meaning hw = diff(edges) rather than hw = mean(diff(centers)) as it is now.