use thin instead of webrick for rack

safari 7.0 on Mavericks was not able to load localhost while using
Webrick as the server. so use thin instead and it seems to work
use vendor prefixed flexbox properties

Safari on Mavericks and on iOS 7 requires the `-webkit` prefix for
flexbox properties. Chrome understands flexbox with or without the
prefix. So, just add the prefix.
add example application for gh-pages. no auth required