add pypalettes to colormapping

[JosephBARBIERDARNAL]

Hi @jbednar !

In this PR I add pypalettes, which is one of the package I maintain at yellow sunflower (a brand new organization I recently created).

On a more or less separate note, I wonder if pyviz is opened to add more specific packages in the "all tools" section? I have many other projects that I think are cool, but they might be too specific for pyviz.org?

I'm mainly thinking:

• pyfonts: working with fonts in matplotlib
• drawarrow: working with arrows in matplotlib
• morethemes: themes for matplotlib
• (there are several others, but they are not considered stable or are chart-specific)

Let me know what you think.

[jbednar]

Thanks for the contribution! Those other libraries sound like they are specifically for Matplotlib users, and as such I'd suggest them for https://matplotlib.org/thirdpartypackages/ rather than a cross-library site like PyViz.

[JosephBARBIERDARNAL]

Ok thanks :)