Expand example 08 with images and captions

- Stereo phone plug (a slight modification of a public domain image
  from https://openclipart.org/detail/192396/headphones-connctor ).
- Cable cross-section drawn to match the wire colors in example 08.
- Make the cable shield color match the one in the cross-section.
- Images for embedding in the connector and cable nodes are stored
  in a new resources folder.

examples/ex08.yml

@@ -7,6 +7,8 @@ connectors:
     pins: [T, R, S]
     pinlabels: [Dot, Dash, Ground]
     show_pincount: false
+    image: ../resources/stereo-phone-plug-TRS.png
+    caption: Tip, Ring, and Sleeve
 
 cables:
   W1:
@@ -14,7 +16,9 @@ cables:
     length: 0.2
     color_code: DIN
     wirecount: 3
-    shield: true
+    shield: SN
+    image: ../resources/cable-WH+BN+GN+shield.png
+    caption: Cross-section
 
 connections:
   -