Squashed 'vendor/assets/javascripts/d3/plugins/' changes from 42102dc..b91ab3e

b91ab3e Simplify slightly.
a9bffba Add inverse for d3.geo.interrupt.
c1bbadd Update README.md
8c8720d Update README.md
0194b7a Update README.md
8f51653 Add another Airy link.
b0f3e73 Add Chamberlin trimetric.
f9d9e5f Fix typo.
8cbf41f Update README.md
8aac1aa Add Airy’s minimum-error azimuthal projection.
20f99cd Update README.md

git-subtree-dir: vendor/assets/javascripts/d3/plugins
git-subtree-split: b91ab3e0efbbc0b25d2946c3727111541de97900
Merge commit '69936db32c89e3b57f902b5466b2d270e99da9aa'

* commit '69936db32c89e3b57f902b5466b2d270e99da9aa':
  Squashed 'vendor/assets/javascripts/d3/plugins/' changes from 42102dc..b91ab3e
Update bundled d3 plugins