asy-brewer: ColorBrewer palettes for Asymptote

Asymptote is vector graphics language for
technical drawing. It ships with a number of base modules including palettes
which provides a number of colour palettes. This module supplements these with
Cynthia Brewer and Mark Hadden’s ColorBrewer palettes (http://colorbrewer2.org/).

The ColorBrewer palettes were designed for maps, allowing effective differentiation
of different colours in neighbouring regions, but they are also useful for other
applications.

HarrowerBrewer2003:
Harrower, Mark, and Cynthia A. Brewer. “ColorBrewer. org: an online tool for
selecting colour schemes for maps.” The Cartographic Journal 40.1 (2003): 27-37.

This module provides three functions returning different types of palettes:

• Sequential: suited to data that ranges from low to high values either on an
  ordinal scale (e.g. cold, warm, hot) or on a numerical scale
• Diverging: used when a critical data class or break point needs to be emphasised
• Qualitative: used for data that does not imply order, but difference in kind

Example Usage:

access brewer;
size(100);
pen[] cols = brewer.Qualitative("Paired", 6);
fill(unitcircle, cols[0]);

Included in this repository is the file demo.asy which gives a further example of
usage of the module which produces the figure below.

Also included in this repository is brewer.json which provides all of the ColorBrewer
palettes in JSON format.