Path.Area: change fromShape() 'start' parameter behavior

'start' used to mean the initial resting position of the tool. Now it
is changed to mean the feed start position.

fromShape() has also improved to automatically guess 'retraction' and
'resume_height' parameters if not given, based on input shape boundary.

src/Mod/Path/App/AppPathPy.cpp

@@ -122,7 +122,7 @@ public:
             "fromShapes(shapes, start=Vector(), return_end=False" PARAM_PY_ARGS_DOC(ARG,AREA_PARAMS_PATH) ")\n"
             "\nReturns a Path object from a list of shapes\n"
             "\n* shapes: input list of shapes.\n"
-            "\n* start (Vector()): optional start position.\n"
+            "\n* start (Vector()): feed start position, and also serves as a hint of path entry.\n"
             "\n* return_end (False): if True, returns tuple (path, endPosition).\n"
             PARAM_PY_DOC(ARG, AREA_PARAMS_PATH)
         );
@@ -415,7 +415,7 @@ private:
         try {
             bool need_arc_plane = arc_plane==Area::ArcPlaneAuto;
             std::list<TopoDS_Shape> wires = Area::sortWires(shapes,&pstart,
-                    &pend, &arc_plane, PARAM_PY_FIELDS(PARAM_FARG,AREA_PARAMS_SORT));
+                    &pend, 0, &arc_plane, PARAM_PY_FIELDS(PARAM_FARG,AREA_PARAMS_SORT));
             PyObject *list = PyList_New(0);
             for(auto &wire : wires)
                 PyList_Append(list,Py::new_reference_to(