Primitives in geometry/curves

Since there is now a distinction between the representation of a primitive and the recognition algorithm, segment computers have been renamed. 

It remains to 
- implements an arithmetical DSS with a,b,mu
- implements an arithmetical DSS with a continued fraction for a/b
- implements a standard DSS in 3d with three 2d DSS
- implements a stabbing line with its preimage
- implements a stabbing circle with a reference circle
- implements a one-balanced word