Implements example basic theme by extending simple theme

I copied this example from [official
documentation](http://docs.getpelican.com/en/3.0/themes.html#example)
Adds twitter bootstrap to the project
Overrides the index template of simple theme

It shows only the article title in a bulleted list. Articles are sorted
in alphabetical order. It removes article summary and other stuff. Just
a plain list of articles titles.