Include pnpoly utility

[johnd0e]

Seen in fix-china-map-offset, layer-count, fly-links

Sources:

• https://github.com/substack/point-in-polygon
• https://github.com/mikolalysenko/robust-point-in-polygon
• https://github.com/rowanwins/point-in-polygon-hao
• https://github.com/metafloor/pointinpoly
• ... https://github.com/topics/point-in-polygon

Ref: #65 (comment)

[le-jeu]

so this is now done in 9729392

[Artoria2e5]

hmm, pretty sure it can be closed -- now that it's moved to global. happy to see my translation of pnpoly get used still. it's the old 1973 code, not one of the new "robust" ones, but... uhhh, i don't think we will be dealing with weirdly large numbers with lat and lngs.

one day we might need to "expand" long polygon vertices into more points on a great-circle approximation, but that day is not today.