Quantizing input before topology construction.

Although no longer required by the exact topology construction implementation,
this seems to be much more tolerant of non-topological inputs.
Move non-topology functions.
Consolidate bounding box computation.
Separate quantization from delta encoding.
Test for closing point.
Add comment re. quantization hashing.
Fix a bug when rotating the current arc.

Wasn’t detecting whether the current arc is already registered or not.