Render and add missing files when running in isolation mode.
Upgrade to Jekyll 2.0

- Use frontmatter defaults for defining layouts.
- Use custom Markdown processor
Improve on-demand rendering process.

- Use Jekyll 2.0's better exclusion filtering
- Use a separate Rack config file to avoid interference from rack/jekyll
Remove layout from news template as it is now set in _config.yml
Correct bug where /index.html wasn't being found
Use my fork of rack-jekyll.
Coerce filenames into UTF-8.

If you don't do this, SafeYAML will write the file name out in base64.
Take care of our own encoding.

LANG and LC_ALL are not set on Jenkins slaves and the build fails
during the bundle installation due to changes in jekyll-rack.  These
changes force the correct encoding to be used during the builds.
Add explanation of how the isolate command can add files on demand.