Add configuration files.

Please note that you should copy staith-config.example.json to
staith-config.json and change the settings in that file as it is not
watched by the version-control system.
Load project-specific files *after* the libraries.
Use the environment settings to filter out drafts in production/test

You can change these settings by either (a) setting the RACK_ENV
environment variable, (b) changing the setting in "staith-config.json",
or (c) changing the values in the file(s) where it is
specified (./serve.rb and ./lib/environment.rb)
Add some comments to ./serve.rb to explain what things mean.