created rectangle struct and IsRect()

defined what a rectangle is and also implemented IsRect(), which returns
a bool whether the coordinates given make a rectangle or not.  Tests
were written for IsRect()

cmd/recty/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"fmt"
+
+	"s.mcquay.me/dm/rect"
+)
+
+func main() {
+	r := rect.Rectangle{
+		P1: rect.Point{1, 1},
+		P2: rect.Point{1, 2},
+		P3: rect.Point{2, 1},
+		P4: rect.Point{2, 2},
+	}
+	fmt.Println(r.IsRect())
+	r1 := rect.Rectangle{
+		P1: rect.Point{0, 0},
+		P2: rect.Point{0, 1},
+		P3: rect.Point{1, 0},
+		P4: rect.Point{1, 1},
+	}
+	fmt.Println(r1.IsRect())
+	r1 := rect.Rectangle{
+		P1: rect.Point{0, 0},
+		P2: rect.Point{0, 1},
+		P3: rect.Point{1, 0},
+		P4: rect.Point{1, 1},
+	}
+	fmt.Println(r1.IsRect())
+}