add stream folder with scan and scan-merge

stream/scan.js

@@ -0,0 +1,14 @@
+//! adapted for mithril from flyd https://github.com/paldepind/flyd
+'use strict'
+
+var combine = require('../stream').combine
+
+module.exports = function (reducer, seed, stream) {
+   var newStream = combine(function (s) {
+    return seed = reducer(seed, s._state.value)
+  }, [stream])
+
+  if (newStream._state.state === 0) newStream(seed)
+
+  return newStream
+}