Fix issue where all points would be considered to be part of plane if the origin is not in the polygon

[mauriciopoppe]

The PR #33 added detection for an edge case where all the points are part of a plane, the detection algorithm was:

1. Compute the initial tetrahedron containing 4 vertices.
2. Taking any 3 vertex from it create a plane.
3. Project all the points towards the plane using dot product, if the dot product is greater than some tolerance (not zero because of float point errors) then it means that a point is not part of plane.

There is an error in (3), let's assume a simple input in 2d where all the points are not in plane.

• [2, 0], [2, 1], [2, -1] (they're points in x=2)
• [1, 0] which is a point in x=1

An ascii diagram:

 1       x
 |
 |
-0---x---x
 |
 |
-1       x
x=0 x=1 x=2

If step (2) detected that all the points in x=2 were part of the plane where the normal is [1, 0] then by following (3) and projecting point [1, 0] to the plane (note that the point is not the normal) would result on it being behind the face and therefore it pass the check and consider the input to be a plane.

The problem in (3) is that we should compare the projection of the point to test [1, 0] to the projection of any plane point to the plane

• project [2, 0] to the plane with a normal [1, 0] is dot([2,0], [1,0]) = 2
• project [1, 0] to the plane with a normal [1, 0] is dot([1,0], [1,0]) = 1
• The diff is 1 and is greater than any tolerance (typically tolerance is a tiny value like 1e-9)

Fixes #38

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.32%. Comparing base (f554dc2) to head (2d1efad).
Report is 32 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   89.36%   90.32%   +0.95%     
==========================================
  Files           6        6              
  Lines         536      620      +84     
  Branches      100      106       +6     
==========================================
+ Hits          479      560      +81     
- Misses         52       55       +3     
  Partials        5        5              

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