introduce locale (as sites subdir and optional param), and...

* use Sinatra 1.3.6
* add short stack trace to error log
* various refactorings
* put Deck file server ahead of Sinatra in middleware chain (using Rack::Cascade)
use subdomain, param, or environment variable to specify locale
TOC now works with locale
Merge pull request #313 from alexch/locale

Locale