Duplicate vertex artifact

mostly copied form the discussion in #34

This is another issue with unnecessarily duplicated vertices which causes this artifact:

There are two verticies at this point:

It seems the deduplication step of the meshing algorithm is not tolerant enough

I think it is caused here, which I was thinking of when I wrote this part:

cx - sx * (1. + EPSILON),
cy - sy * (1. + EPSILON),
cz - sz * (1. + EPSILON),

When checking for duplicates sx = 1e-5
sx * (1. + EPSILON) = 1e-5*( 1+1e-5) = 1.00001e-05 which is 6sf so it is fine`
cx is the coordinate center which could be anything lets say 123.0
cx + 1.00001e-05 = 123.0 + 1.00001e-05 = 123.00001 Which is 8 sf too many sf for f32
Truncating previous to 6sf we get 123.000 which is equivalent boundary size of 0.
Which means if there is any rounding error in the coordinate it won't be treated as duplicate

norman784 / gaiku