document image options (#35)

quad/quad/scribblings/quad.scrbl

@@ -562,6 +562,15 @@ Whether the block is hyphenated. Activated only when value is @racket["true"].
 Whether the contents of the block are clipped to its boundary. Activated only when value is @racket["true"]. 
 }
 
+@deftogether[(@defthing[#:kind "attribute" image-file symbol?]
+              @defthing[#:kind "attribute" image-alt symbol?]
+              @defthing[#:kind "attribute" image-height symbol?]
+              @defthing[#:kind "attribute" image-width symbol?])]{
+Specify a quad with an image (either @racket{.png} or @racket{.jpeg}). @racket[image-file] is a string containg the path to the image file. @racket[image-alt] is optional text. 
+
+@racket[image-height] and @racket[image-width] are optional sizing values, each of which is a @tech{dimension string}. If neither @racket[image-height] nor @racket[image-width] are provided, the image is displayed at ``full size'' (meaning one pixel = one point, or 72 dpi). If both @racket[image-height] and @racket[image-width] are provided, the image is displayed at exactly that size. If only @racket[image-height] or @racket[image-width] is provided, the image is scaled by the proportion implied by the value. That is, if @racket[image-height] is @racket{50} and the image is 200 pixels high by 100 pixels wide, then the image will be displayed 50 pixels high by 25 pixels wide.
+}
+
 @subsubsection{Other attributes}
 
 @deftogether[(@defthing[#:kind "attribute" font-size symbol?]

quad/quadwriter/attrs.rkt

@@ -136,7 +136,7 @@ Naming guidelines
 
                            line-wrap
 
-                           image-data
+                           image-file
                            image-object
                            image-alt
                            image-height

quad/quadwriter/layout.rkt

@@ -97,7 +97,7 @@
 (define (generic->typed-quad q)
   (cond
     [(line-break-quad? q) q]
-    [(match (quad-ref q :image-data)
+    [(match (quad-ref q :image-file)
        [#false #false]
        [(? file-exists? path-string)
         (define img-obj (open-image (current-pdf) path-string))

quad/quadwriter/tags.rkt

@@ -35,7 +35,7 @@
           :line-height "false"
           :image-height "150"
           :line-align-last "center" ; need `last` because img is a block-level element.
-          :image-data (second (assq 'src attrs))
+          :image-file (second (assq 'src attrs))
           :image-alt (second (assq 'alt attrs))
           :display "block") exprs))