add a new subcurve class (parametric subcurve) and a joincurve (concatenate curves)

- bug fix in curves (the subcurve function return bad path in case of start and end both on the same segment)

- correction d'un bug lorsqu'une subcurve etait créee avec startPoint=endPoint (les curves cycliques ne fonctionnaient pas dans tous les cas)

second move to a MVC design

add a OE_svgParser class to fill the document
first move to a MVC design

- for closed curves (now the function loop when the start point is after the end point)
- add a rev param to reverse the curve sens

subcurve only work if start<end for now