Add m.redraw() support for multiple mount points

To better match `0.2.x` behavior: https://jsfiddle.net/xbpyqL9k/

api/redraw.js

@@ -0,0 +1,12 @@
+"use strict"
+
+module.exports = function(renderers) {
+    return function() {
+        if (renderers.length === 0) return
+        if (renderers.length === 1) return renderers[0]()
+        
+        for (var i = 0; i < renderers.length; i++) {
+            renderers[i]()
+        }
+    }
+}