Added threshold example

exampleThreshold.js

+$(function () {
+    		
+    	//<div id="flotOrig" style="width: 800;height: 400;"></div>
+	
+    		
+    	var d1 = [[20,20], [42,60], [54, 20], [80,80]];
+  
+		var options = { series: {
+							curvedLines: {
+										active: true
+							},
+							threshold: { below: 40, color: "rgb(0, 0, 0)" }
+						},
+						axis: { min:10, max: 100},
+						yaxis: { min:10, max: 90}
+   						};
+									
+		$.plot($("#flotOrig"), [{data: d1, lines: { show: true, lineWidth: 3}, curvedLines: {apply:true}}, {data: d1,  points: { show: true }}], options);
+});
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