polyfill missing hexagons near pentagons

[Pessimistress]

Demo: https://uber-common-public.s3-us-west-2.amazonaws.com/svc-vis-prototype/h3-grid/index.html

The app calls h3.polyfill to get hexagons that fill each OSM tile. The offending tiles here are

{
  "x": 87,
  "y": 153,
  "z": 8,
  "east": -56.25,
  "north": -33.13755119234615,
  "south": -34.30714385628804,
  "west": -57.65625,
}

{
  "x": 86,
  "y": 154,
  "z": 8,
  "east": -57.65625,
  "north": -34.30714385628804,
  "south": -35.4606699514953,
  "west": -59.0625,
}

Though the issue is observed at multiple zoom levels.

[nrabinowitz]

This PR provides a slow but correct fix to the core lib: uber/h3#279

There's discussion in that PR about a faster, also correct algorithm that we plan to implement soon. If that gets a PR from @dfellis in the near term, we'll probably wait for it to land before the next release; otherwise, we'll release the slow version, which should fix this issue.

[nrabinowitz]

Fixed in #74