Add example site.

* .gitignore: Ignore example build artifacts.
* example/haunt.scm: New file.
* example/posts/foo.sxml: New file.
* example/posts/bar.html: New file.

.gitignore

@@ -11,3 +11,4 @@
 *~
 .#*
 /haunt/config.scm
+/example/site/