added support for the 'site::html_file_extensions' option in config.yml: the set of specified, comma-separated extensions will be renamed to .html in the generated output when pretty_urls is `false`. This is a quick way to, for example, convert input MarkDown files with extension `.md` or `.markdown` to `.html` output files.

Example config.yml:

  site:
      title: Your New PieCrust Website
      description: A sample website running with PieCrust
      author: Anonymous
      pretty_urls: false
      html_file_extensions: md,markdown,textile

  smartypants:
      enable: true

  baker:
      skip_patterns:
          - /^index.php/