Perceive extended tetrahedral from 2D/3D coordinates.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Perceive allene stereochemistry from 2D and 3D depictions.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Clockwise sort should handle exactly opposite atoms.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Explicit hydrogens invert winding.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Improved winding detection for tetrahedral centres.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Improved identification of tetrahedral elements. More improvements needed but now any non-planar bonds indicate a tetrahedral centre should be created in 2D depictions. In 3D depictions, we check the environment of each neighbour. The method is currently inadequant and fails to identifier interdependent stereocentres (as seen in test) but is required to avoid create tetrahedral configurations for non-stereogenic atoms (i.e. methane).

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>