added method to determine distance between points

should be valuable to know what distance between two points is. Also
added testing

point.go

@@ -1,5 +1,11 @@
 package rect
 
+import "math"
+
 type Point struct {
 	X, Y float64
 }
+
+func distance(p1, p2 Point) float64 {
+	return math.Sqrt(math.Pow((p1.X-p2.X), 2) + math.Pow((p1.Y-p2.Y), 2))
+}

point_test.go

@@ -0,0 +1,29 @@
+package rect
+
+import (
+	"math"
+	"testing"
+)
+
+func TestDistance(t *testing.T) {
+	var distanceTest = []struct {
+		p        []Point
+		expected float64
+	}{
+		{[]Point{Point{1, 1}, Point{4, 5}}, 5},
+		{[]Point{Point{-1, -1}, Point{2, 3}}, 5},
+		{[]Point{Point{1, 1}, Point{2, 2}}, math.Sqrt(2)},
+		{[]Point{Point{1, 1}, Point{40, 20}}, math.Sqrt(1882)},
+	}
+	for _, rt := range distanceTest {
+		actual := distance(rt.p[0], rt.p[1])
+		if actual != rt.expected {
+			t.Errorf(
+				"failed spiral:\n\texpected: %d\n\t  actual: %d",
+				rt.expected,
+				actual,
+			)
+		}
+
+	}
+}