Support z-coordinate as input for @turf/pointplane

[dpmcmlxxvi]

Addresses #628 for @turf/pointplane. PR has the following edits:

• Uses z-coordinate if triangle properties a, b, or c are undefined. So, should be backwards compatible.
• Replaces original test with simpler more meaningful test values. Besides, original test was only testing for a truthy response. Using simpler coordinates seemed easier to verify.
• Updated test.js and bench.js syntax to ES6.

@DenisCarriere Let me know if this is what you had in mind.

---

Please fill in this template.

• Use a meaningful title for the pull request. Include the name of the package modified.
• Have read How To Contribute.
• Run npm test at the sub modules where changes have occurred.
• Run npm run lint to ensure code style at the turf module level.

[DenisCarriere]

@dpmcmlxxvi 👍 Yep that's what I had in mind to support Z coordinates.

My last commit added Geometry support using @turf/invariant to normalize the input.

[DenisCarriere]

Looks good!

[dpmcmlxxvi]

@DenisCarriere Thanks for the review/edits. On the inputs, it now accepts an array for the input point. I thought the general philosophy of Turf was to have only GeoJSON as input and output for geographical features.

[DenisCarriere]

@dpmcmlxxvi Agreed, however the Point is the only exception since many times your point data will consist of [x, y] and not be in a Geometry/Feature (it's a pain having to convert your point data to Geometry or Feature if the only valid input is a point).

Rules to allow Array<number>

If the input is ONLY a point and you must use getCoord method from @turf/invariant which applies point validation.