ACF2 HTTP Protocol
==================

Load JavaScript client:
req: GET /

Start transaction:
req: POST /
resp: txn ID (in header as X-ACF-Transaction-ID)
      - use X-ACF-Transaction-ID in the header of any subsequent
      	request to process it in the transaction's context

Commit transaction:
req: POST /
     X-ACF-Transaction-ID: <txn_id>

Abort transaction:
req: DELETE /
     X-ACF-Transaction-ID: <txn_id>

Get object:
req: GET /config/<obj_path>
resp: JSON object, with the following attributes:
      data: JSON serialization of object
      	    - primitive types as JSON primitives
      	    - references as path names (relative to scope)
      	    - models and collections as JSON objects or arrays with
	      members as attributes:
      	    - primitive members as JSON primitives
      	    - reference, model, and collection members as path names
      meta: JSON object, with the following attributes
      	    - name (last component of path name)
      	    - ui-name (shown to user)
      	    - description (optional help text)
      	    - type (e.g. model, collection, reference, string, number,
	      boolean)
      	    - widget (name of client-side JS module used to display
	      the data)
      	    - required (boolean)
      	    - max-length
      	    - choices (optional array of allowed values)
      	    - ui-choices (user-friendly choices to be shown in combo
	      boxes)
      	    - fields (model only): array of field metadata JSON
	      objects
      	    - members (collection only): metadata for members (JSON
	      object)
      	    - scope (references only): subtree where the reference can
	      refer to

Create/update object:
req: PUT /config/<obj_path>
     - body shall contain the object serialized as the data attribute
       in GET responses
     - undefined model attributes are deleted

Delete object:
req: DELETE /config/<obj_path>

Invoke object-specific action (not yet supported by server):
req: POST /config/<obj_path>/<action>
     - arguments passed as a JSON array in body; serialization as in
       GET responses
resp: action-specific JSON
      - for time-consuming actions, can return multiple JSON
      	documents, each containing a status update