https://github.com/d3/d3-shape/releases/tag/v3.1.0

Add d3.symbolsStroke.
Add d3.symbolsFill, replacing (deprecating) d3.symbols.
Add d3.symbolAsterisk.
Add d3.symbolDiamond2.
Add d3.symbolPlus.
Add d3.symbolSquare2.
Add d3.symbolTriangle2.
Add d3.symbolX.
Add d3.link.

d3.rank can now take a comparator in addition to an accessor

We don't need to change anything for "d3.rank, d3.sort, d3.bisector, and d3.groupSort now require comparators to have exactly two arguments", since that's how it was already typed (even though the code was actually more lax).

note: I'm not sure that the path function must have 3 arguments; most of the time people will use only 1 argument

- add rgb.clamp and hsl.clamp
- add color.formatHex8