added comments

images.go

@@ -13,6 +13,8 @@ import (
 	"github.com/tfriedel6/canvas/backend/backendbase"
 )
 
+// Image is a type holding information on an image loaded with the LoadImage
+// function
 type Image struct {
 	src      interface{}
 	cv       *Canvas

path2d.go

@@ -4,6 +4,8 @@ import (
 	"math"
 )
 
+// Path2D is a type that holds a predefined path which can be drawn
+// with a single call
 type Path2D struct {
 	cv    *Canvas
 	p     []pathPoint