New find method "find_from_metrics". 

This makes it possible to find metrics based on graphite calculations, f. ex.
highestCurrent(exclude(collectd.*.ping.ping-responder_example_com,50). This is not possible through  the "/find" endpoint and "graphite.metric" expects one specific time series metric. The following example will return the 50 highest RTT times towards a central server (collected by collectd):

```javascript
var graph_regex = "highestCurrent(collectd.*.ping.icmp-beacon_example_com,50)";

graphite.find_from_metrics(graph_regex, function(error, results) {
   metrics = results.sort().map(function(i) {
       var s = i.split(".");
       return graphite.metric(i)
              .alias(s[1])
              .summarize("avg");
   });
   for (var i=0;i<metrics.length;i++) { 
     d3.select("#graphs").call(function(div) {
     div.append("div").selectAll(".horizon")
        .data([metrics[i]])
       .enter().append("div")
       .attr("class", "horizon")
       .call(context.horizon());
     });
   };
});
```