Map colormap of data

[tdegeus]

Here is a first proposal @davidbrochart . Please feel free to comment.

This allows for the following

    auto c = cppcolormap::Greys(5);
    xt::xtensor<double, 1> data = {0, 1, 2, 3, 4};
    std::cout << cppcolormap::as_colors(data, c) << std::endl;

Fixes #24

P.S. I should probably introduce tests. In contrast to the colormaps this is something that could actually go wrong.

[davidbrochart]

I just tried it on a real use-case, and it works great 👍
Thanks a lot!

[tdegeus]

@davidbrochart I simplified the implementation a bit (same API). I was just doubting for a second if the name could be improved. However, I don't have good ideas. Do you still have suggestions?

[davidbrochart]

The only thing I can think of is map_colors, but as_colors is fine too.