Adds matrix sub package & adds polynomial regression series (#36)

* updates

* updates

* tests.

* test coverage

* fixing test

* stride not rows + cols

* lu decomp implementation.

* poly regression!

* poly regression works.

* typo.

_examples/poly_regression/main.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"net/http"
+
+	"github.com/wcharczuk/go-chart"
+)
+
+func drawChart(res http.ResponseWriter, req *http.Request) {
+
+	/*
+		In this example we add a new type of series, a `PolynomialRegressionSeries` that takes another series as a required argument.
+		InnerSeries only needs to implement `ValueProvider`, so really you could chain `PolynomialRegressionSeries` together if you wanted.
+	*/
+
+	mainSeries := chart.ContinuousSeries{
+		Name:    "A test series",
+		XValues: chart.Sequence.Float64(1.0, 100.0), //generates a []float64 from 1.0 to 100.0 in 1.0 step increments, or 100 elements.
+		YValues: chart.Sequence.Random(100, 100),    //generates a []float64 randomly from 0 to 100 with 100 elements.
+	}
+
+	polyRegSeries := &chart.PolynomialRegressionSeries{
+		Degree:      3,
+		InnerSeries: mainSeries,
+	}
+
+	graph := chart.Chart{
+		Series: []chart.Series{
+			mainSeries,
+			polyRegSeries,
+		},
+	}
+
+	res.Header().Set("Content-Type", "image/png")
+	graph.Render(chart.PNG, res)
+}
+
+func main() {
+	http.HandleFunc("/", drawChart)
+	http.ListenAndServe(":8080", nil)
+}