examples, some fixes

examples/custom_formatters/main.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+	/*
+	   In this example we use a custom `ValueFormatter` for the y axis, letting us specify how to format text of the y-axis ticks.
+	   You can also do this for the x-axis, or the secondary y-axis.
+	   This example also shows what the chart looks like with the x-axis left off or not shown.
+	*/
+
+	graph := chart.Chart{
+		YAxis: chart.YAxis{
+			Style: chart.Style{
+				Show: true,
+			},
+			ValueFormatter: func(v interface{}) string {
+				if vf, isFloat := v.(float64); isFloat {
+					return fmt.Sprintf("%0.6f", vf)
+				}
+				return ""
+			},
+		},
+		Series: []chart.Series{
+			chart.ContinuousSeries{
+				XValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+				YValues: []float64{1.0, 2.0, 3.0, 4.0, 5.0},
+			},
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	graph.Render(chart.PNG, res)
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	http.ListenAndServe(":8080", nil)
+}