Fix making of "sources.html"

Uses same template as synopsis, maybe this shoudl be generalised a bit

doc/.gitignore

@@ -0,0 +1,8 @@
+synopsis/index.txt
+synopsis/index.html
+synopsis/api-examples-*.txt
+synopsis/api-examples.gfs
+synopsis/categories-imagemap.html
+synopsis/categories.png
+
+gfdoc/sources.html