anchor.diff:  - create initial doc with example entity CRUD
   ### 0.0.1 (01/03/2016) mlo
   - synchronize with github repository, branch: documentation
  -
  +### 0.0.1 (01/03/2016) mlo
  +- resources to create or update shouldn't have id
  +- document HTTP 400 bad request response
   
   ## TODO
  -- Document CRUD for deck, flashcard, stat
  +- Document CRUD for stat
  +
  +# Client errors
  +
  +Response with HTTP code different then **2xx** family should be treated as a failure response. 
  +By default API return response with HTTP code **4xx** family.
  +
  +### Example HTTP 400 Bad request response:
  +```
  +{
  +    "code": "E001",
  +    "message": "Id cannot be null"
  +}
  +```
   
   # Group Deck
   
  
positive.code: 
  + Request (application/json)
  
      + Attributes (Flashcard)
  
  + Response 200 (application/json)
  
      This response is returned when flashcard was updated.
      
      + Attributes (Flashcard)
  
  + Response 400 (application/json)
  
      This response is returned when flashcard validation failed.
  
      + Body
  
  ### Remove Flashcard [DELETE /decks/{deckId}/flashcards/{flashcardId}]
  
  
negative.code: ## FlashcardCollection (array)
  + 0: (Flashcard)
  + 1: (Flashcard)
  + 2: (Flashcard)
  
  ## BadRequestResponse (object)
  + code: `E001` (string, required) - TODO sample error code
  + message: `Id cannot be null` (string, required) - TODO sample error message - human readable