Add order= parameter

[adkabo]

Currently the plot depends on row order which leads to weird plots. So I have to sort the data before putting it into AoG. I don't like that the algebra depends on the row order. Instead I would like an order parameter in the mapping.

using DataFrames, RDatasets, AlgebraOfGraphics

diamonds = dataset("ggplot2", "diamonds")

data(diamonds) * mapping(:X, :Price) * visual(Lines) |> draw

data(sort(diamonds, :X)) * mapping(:X, :Price) * visual(Lines) |> draw

data(diamonds) * mapping(:X, :Price, order=:X) * visual(Lines) |> draw

[roland-KA]

This may be related to Issue #262.