Relations can now take values

When defining relations, you can now specify a static value to check
against.  For example:
````json
"relations": [
  {
    "column": "fancy_id",
    "inverse": "id"
  },
  {
    "column": "fancy_type",
    "value": "FNCY"
  }
]
````

This is primarily useful for objects with polymorphic associations where
the associating ID is not guaranteed to be unique.
Pool size can now be specified in the config

Specifically, it can be specified in the databaseServer block.
Example:
````json
"pool": {
  "min": 2,
  "max": 20
}
````