add ironing angle (#2320)

src/libslic3r/PrintConfig.cpp

@@ -2375,6 +2375,16 @@ def = this->add("filament_loading_speed", coFloats);
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionFloat(20));
 
+    def           = this->add("ironing_angle", coFloat);
+    def->label    = L("Ironing angle");
+    def->category = L("Quality");
+    def->tooltip  = L("The angle ironing is done at. A negative number disables this function and uses the default method.");
+    def->sidetext = L("°");
+    def->min      = -1;
+    def->max      = 359;
+    def->mode     = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(-1));
+
     def = this->add("layer_change_gcode", coString);
     def->label = L("Layer change G-code");
     def->tooltip = L("This gcode part is inserted at every layer change after lift z");