Allow multiple config files (also slight tweak to format)

* Multiple config files can be listed on the command line and they'll
  be merged together. This allows you to put each app into its own
  file with one database specified, but still start up a server running
  multiple apps/databases.
* To make this work smoothly, the "databases" property is now an object
  instead of an array. The database name is the key of the entry
  instead of a "name" property.