Make setMarker public API

c3.js

@@ -3429,6 +3429,10 @@
         $$.config.marker_types[id] = type;
     }
 
+    c3_chart_fn.setMarker = function(id, type){
+        return this.internal.setMarker(id, type);
+    }
+
     c3_chart_internal_fn.getMarker = function(d, i){
         var $$ = this;
 

src/marker.js

@@ -136,6 +136,10 @@ c3_chart_internal_fn.setMarker = function(id, type){
     $$.config.marker_types[id] = type;
 }
 
+c3_chart_fn.setMarker = function(id, type){
+    return this.internal.setMarker(id, type);
+}
+
 c3_chart_internal_fn.getMarker = function(d, i){
     var $$ = this;