DSLSsubsegment release

Class DSLSubsegment including several algorithms to compute the minimal characteristics of a subsegment of a DSL of known characteristics:
- Algorithm using the Farey fan + extension when the DSL characteristics are floating-point numbers
- Algorithm using the local convex hull computation. 
- Short example file
- Big test file including comparison with ReversedSmartDSS and ArithmeticalDSS algorithms

Class ArithDSSIterator: an iterator over the points of a DSS of given characteristics from a given first point. Used in the test file mentioned above to compute the minimal characteristics of a subsegment using the ArithmeticalDSS algorithm.