trying to regularize page URL structure

As described here: http://jekyllrb.com/docs/github-pages/#project-page-url-structure

_config.yml

@@ -1,7 +1,8 @@
 name: Programming Historian
 description: Introductory and intermediate programming lessons for humanists
 url: http://programminghistorian.org
+baseurl: /jekyll
 permalink: :title
 safe: true
 pygments: true
-markdown: kramdown
+markdown: kramdown