allow plain app to be used as site index

By implementing the `index` method, it can be used for a site index. We
need to address this more generally.

Refs #141
add new index page for introduction to Statocles

This moves the blog to a subsection of the site which we can use for
releases and notifications.
remove test post
add initial release announcement
always use utf-8 when reading/writing files

This fixes the "wide character in print" warnings and is generally a
good idea anyway.

Fixes #140