resolves asciidoctor#242 scale down SVG if width is wider than page

lib/asciidoctor-pdf/converter.rb

@@ -793,7 +793,15 @@ def convert_image node
     when 'svg'
       begin
         svg_obj = ::Prawn::Svg::Interface.new (::IO.read image_path), self, position: position, width: width
-        actual_w = svg_obj.document.sizing.output_width
+        # FIXME would be nice of prawn-svg accepted a max width argument
+        if !width && (actual_w = svg_obj.document.sizing.output_width) > bounds.width
+          # TODO would be nice to have a recalculate method w/ a new requested width and/or height
+          #svg_obj.document.sizing.requested_width = bounds.width
+          #svg_obj.document.sizing.calculate
+          # instead we'll just reconstruct
+          svg_obj = ::Prawn::Svg::Interface.new (::IO.read image_path), self, position: position, width: bounds.width
+          actual_w = svg_obj.document.sizing.output_width
+        end
         actual_h = svg_obj.document.sizing.output_height
         rel_left = { left: 0, right: (bounds.width - actual_w), center: ((bounds.width - actual_w) / 2.0) }[position]
         # TODO layout SVG without using keep_together (since we know the dimensions already); always render caption