All remaining subcommands for the h3 cli program

[dfellis]

After implementing the region subcommands, all of the rest documented on h3geo.org were "trivial" as all patterns of subcommand had been implemented, so I just slogged through writing all of them while I had the drive to do it. ;)

There may be some test failures with degsToRads and friends due to floating point rounding errors on different CPU architectures. I hope not, but if so, then I'll have to figure out how to test them better.

• areNeighborCells
• cellsToDirectedEdge
• isValidDirectedEdge
• getDirectedEdgeOrigin
• getDirectedEdgeDestination
• directedEdgeToCells
• originToDirectedEdges
• directedEdgeToBoundary
• cellToVertex
• cellToVertexes
• vertexToLatLng
• isValidVertex
• degsToRads radsToDegs
• getHexagonAreaAvgKm2
• getHexagonAreaAvgM2
• cellAreaRads2
• cellAreaKm2
• cellAreaM2
• getHexagonEdgeLengthAvgKm
• getHexagonEdgeLengthAvgM
• edgeLengthKm
• edgeLengthM
• edgeLengthRads
• getNumCells
• getRes0Cells
• getPentagons
• pentagonCount
• greatCircleDistanceKm
• greatCircleDistanceM
• greatCircleDistanceRads
• describeH3Error

[dfellis]

Oh, this currently includes the region subcommands in this PR, since it depends on that one, but once it gets approved and merged, this'll be reduced to only the new commands.

I did (almost) every command in a separate commit, for easier reviewing.

[coveralls]

coverage: 98.782%. remained the same when pulling d63accfd1d5c164b339fb38d5643f16d1d171295 on h3-cli-remaining-subcommands into 33681ff65bc4bb4a3addf8dbef5c6b070f811b27 on master.

[dfellis]

Discussed offline, some of the inconsistencies will be taken care of in a follow-up PR.