Palette feature request

[andy-esch]

Sometimes its important to associate a palette with specific values. This can be done with color_category_style but it feels laborious:

palette = {
    "Residential": "blue",
    "Commercial": "yellow",
    "BPP,Commercial": "orange",
    "BPP,Residential": "purple",
    "BPP,Commercial,Residential": "white",
    "Commercial,Residential": "green",
    "BPP": "red",
}

Layer(
    polys,
    color_category_style(
        "usedesc", palette=list(palette.values()), cat=list(palette.keys())
    ),
)

It'd be really nice if we could directly pass in palette to the palette argument like so:

Layer(
    polys,
    color_category_style("usedesc", palette=palette),
)

This is more inline with what seaborn and other libraries do:

Besides this, I've had issues with passing different iterables into the palette and cat kwargs above. I had to cast them to list for it to work. Extracting the keys and values from the dictionary (palette.keys() and palette.values()) gave me the following errors after passed them in:

IMO most iterables should work as arguments here (excluding str type)