Having the initial rank threshhold too low caused them to sometimes
loop around and become negative, causing problems later down the line.
This sets the rank of the "entry" node to 4 offsetting the possible
causes of this issue quite a bit.
(the following is the original commit message)
Preparation includes:
- ensuring there are no loops.
- ensuring there are no edges spanning more than a single layer.
- ensuring there are no backwards facing edges that were not split
into a bunch of parts to simplify laying them out.
- ensuring there are no self loops (they are treated similarly to
backwards facing edges, which they theoretically are).
Subproducts include:
- `Classifier` allowing to cheaply determine whether a given node is
adjacent to an artificial edge.
- `Ranks` container allowing to easily determine the layer each of the
nodes belongs to.
Ivan Krysak