adjust image docs to use svg instead of png

pkgs/htdp-pkgs/htdp-doc/teachpack/2htdp/scribblings/image-guide.scrbl

@@ -12,7 +12,9 @@
           "img-eval.rkt"
           scribble/decode
           scribble/manual
-          scribble/eval)
+          scribble/eval
+          scribble/core
+          scribble/html-properties)
 
 @(define guide-eval (make-img-eval))
 
@@ -35,8 +37,8 @@
 @(interaction-eval #:eval guide-eval 
                    (require racket/list racket/local))
 
-
+@title[#:style (style "svg" (list (render-pict-as 'svg-images)))
-@title[#:tag "image-guide"]{Image Guide}
+               #:tag "image-guide"]{Image Guide}
 
 This section introduces the @racketmodname[2htdp/image] library
 through a series of increasingly complex image constructions

pkgs/htdp-pkgs/htdp-doc/teachpack/2htdp/scribblings/image.scrbl

@@ -34,7 +34,7 @@
      (img-eval '(extra-margin 0))))
      
 
-@teachpack["image"]{Images}
+@teachpack[#:svg? #t "image"]{Images}
 
 @(define mode/color-and-nitty-text
    (make-splice

pkgs/htdp-pkgs/htdp-doc/teachpack/htdp/scribblings/shared.rkt

@@ -1,12 +1,17 @@
 #lang racket/base
 
-(require scribble/manual)
+(require scribble/manual 
+         scribble/core
+         scribble/html-properties)
 
 (provide teachpack
          beginner-require)
 
-(define (teachpack tp . name)
+(define (teachpack #:svg? [svg? #f] tp . name)
   (apply title #:tag tp
+         #:style (if svg? 
+                     (style "svg" (list (render-pict-as 'svg-images)))
+                     #f)
          `(,@name ": " ,(filepath (format "~a.rkt" tp))
            ,(index (format "~a teachpack" tp)))))