Expose outside and root diameter to freecad

The values are already calculated by pygear and this change make them
available as properties in FreeCAD.
The naming should be in line with the rest of fcgear's nomenclature,
derived from https://qtcgears.com/tools/catalogs/PDF_Q420/Tech.pdf

freecad/gears/features.py

@@ -122,6 +122,10 @@ class InvoluteGear(BaseGear):
                         "gear", "gear_parameter", "test")
         obj.addProperty("App::PropertyLength", "dw",
                         "computed", "pitch diameter", 1)
+        obj.addProperty("App::PropertyLength", "da",
+                        "computed", "outside diameter", 1)
+        obj.addProperty("App::PropertyLength", "df",
+                        "computed", "root diameter", 1)
         obj.addProperty("App::PropertyLength", "transverse_pitch",
                         "computed", "transverse_pitch", 1)
         obj.gear = self.involute_tooth
@@ -188,6 +192,8 @@ class InvoluteGear(BaseGear):
 
         # computed properties
         fp.dw = "{}mm".format(fp.gear.dw)
+        fp.da = "{}mm".format(fp.gear.da)
+        fp.df = "{}mm".format(fp.gear.df)
         fp.transverse_pitch = "{}mm".format(fp.gear.pitch)
 
     def __getstate__(self):