Add support for changing markers after chart creation

src/marker.js

@@ -121,4 +121,14 @@ c3_chart_internal_fn.getMarker = function(d, i){
     var func = marker_fn[$$.config.marker_types[d.id]];
     
     return func($$.pointR(d, i), $$.color(d, i)).node();
-};
\ No newline at end of file
+};
+
+c3_chart_fn.dataMarker = function(id, value){
+    var $$ = this.internal;
+    if(typeof value !== 'string') {
+        return $$.config.marker_types[id];
+    }
+    if($$.config.marker_types[id] !== value){
+        $$.config.marker_types[id] = value;
+    }
+};

src/shape.line.js

@@ -292,6 +292,7 @@ c3_chart_internal_fn.generateGetAreaPoints = function (areaIndices, isSub) { //
 
 c3_chart_internal_fn.updateCircle = function () {
     var $$ = this;
+    $$.main.selectAll('.' + CLASS.circles).selectAll('.' + CLASS.circle).remove();
     $$.mainCircle = $$.main.selectAll('.' + CLASS.circles).selectAll('.' + CLASS.circle)
         .data($$.lineOrScatterData.bind($$));
     $$.mainCircle.enter().append($$.getMarker.bind($$))