lsMakeGeometry fails for cylinder with small grid delta using float

[tobre1]

lsMakeGeometry produces a wrongly meshed cylinder when using a grid delta < 0.5 and floating point single precision. The problem stems from the function lsConvexHull, which does not work well with multiple points lying on the same plane.

Possible solution: create simple mesh manually for the cylinder.

[XaverKlemenschits]

This problem was NOT fixed in #70, since the problem stems from a numerical issue during lsFromSurface mesh, which determines a point lying outside the cylinder as inside and thus creates a faulty level set. This is not a problem for double precision though.