message: Update API in plugged SP design.
diff: @@ -18,17 +18,18 @@ A plugin should provide handler to parse custom reply to fixed data structure.
  The signature of the handler is described below together with custom `free` call to deallocate result data.
  ```rust
  -extern fn custom_transaction_parser(reply_from_node: *const c_char, parsed_sp: *mut *const c_char) -> ErrCode;
  -extern fn custom_free(data: *mut c_char) -> ErrCode;
  +extern fn CustomTransactionParser(reply_from_node: *const c_char, parsed_sp: *mut *const c_char) -> ErrorCode;
  +extern fn CustomFree(data: *mut c_char) -> ErrorCode;
  ```
  Libindy API will contain call to register handler for specific transaction type:
  ```rust
  extern fn indy_register_transaction_parser_for_sp(command_handle: i32,
  + pool_handle: i32,
  txn_type: *const c_char,
  - parser: custom_transaction_parser,
  - free: custom_free,
  - cb: extern fn(command_handle_: i32, err: ErrCode)) -> ErrCode;
  + parser: CustomTransactionParser,
  + free: CustomFree,
  + cb: extern fn(command_handle_: i32, err: ErrorCode)) -> ErrorCode;
  ```
  ### Parsed Data structure
  