migrate posts to AsciiDoc, templates to slim

- switch to Awestruct 0.5.0
- switch to asciidoc, migrate styles to bootstrap 2.1
- use AsciiDoc extension supported on GitHub (.adoc)
- set imagesdir for GitHub preview
- remove disqus fixer hack
- use awestruct- prefix in header attributes, formatting
- update to Asciidoc 0.1.1
- upgrade to Ruby 2.0.0
- add comment about secure environment variables
- switch templates to slim, add asciidoctor config, fix pagination
- use + instead of ` for inline literal
- update ignored files
- move date into doc, add index
- use default layout for posts
- update revdate to reflect timezone at time of post
- add twitter card, wrap post date in time element
- use iso date in blog post
- add task to automatically set publish dates
- remove tz_offset import
- custom atom feed