Add SET support.

Squashed commit compiled from #7. All work by @kureikain.

Fixes #7.

README.md

@@ -77,10 +77,6 @@ file and restart the StatsD process.
 
 ## Unsupported Metric Types
 
-#### Flush Strategy
-
-* Sets
-
 #### Proxy Strategy
 
 * Counter with sampling.
@@ -92,6 +88,40 @@ file and restart the StatsD process.
 StatsD packets are currently mapped to the following InfluxDB events. This is
 a first try and I'm open to suggestions to improve this.
 
+### Set
+
+StatsD package `client_version:1.1|c`, `client_version:1.2|c` as Influx event:
+
+```js
+[
+  {
+    name: 'visior',
+    columns: ['value', 'time'],
+    points:  [['1.1', 1384798553000], ['1.2', 1384798553001]]
+  }
+]
+```
+
+If you are using Grafana to visualize a Set, then using this query or
+something similar
+
+```
+SELECT version, count(version) FROM client_version GROUP BY version, time(1m)
+```
+
+Also, to count for the size of unique value, another InfluxDB event is
+also pushed
+
+```js
+[
+  {
+    name: 'visitor_count',
+    columns: ['value', 'time'],
+    points:  [set.length, 1384798553001]
+  }
+]
+```
+
 ### Counter
 
 StatsD packet `requests:1|c` as InfluxDB event:

lib/influxdb.js

@@ -122,12 +122,25 @@ InfluxdbBackend.prototype.logDebug = function (msg) {
   }
 }
 
+/**
+ * Flush strategy handler
+ *
+ * @param {Number} timestamp
+ * @param {Object} stats metric
+ */
 InfluxdbBackend.prototype.processFlush = function (timestamp, metrics) {
   var self = this,
       counters = metrics.counters,
       gauges = metrics.gauges,
       timerData = metrics.timer_data,
       points = [],
+      sets  = function (vals) {
+        var ret = {};
+        for (var val in vals) {
+          ret[val] = vals[val].values();
+        }
+        return ret;
+      }(metrics.sets),
       key, timerKey;
 
   /* Convert timestamp from seconds to milliseconds. */
@@ -145,6 +158,13 @@ InfluxdbBackend.prototype.processFlush = function (timestamp, metrics) {
     }
   }
 
+  for (set in sets) {
+    sets[set].map(function (v) {
+      points.push(self.assembleEvent(set, [{value: v, time: timestamp}]));
+    })
+    points.push(self.assembleEvent(set + "_count", [{value: sets[set].length, time: timestamp}]));
+  }
+
   for (key in gauges) {
     var value = gauges[key],
         k = key + '.gauge';