ExecQuery implements general query method for Datastore.

UseAppengineContext replace Bubble.Context by appengine's context.Context.

UseReqRespLogger logging request & response value.

HTTPError is response JSON.

IntIDInPathReq is int id request for in path value.

IntIDReq is int id request for in query value.

Noop is no-op.

ReqListOptions is request that use for list query options.

RespListOptions is response of list query.

StringIDReq is string id request for in query value.

QueryListLoader interface is automagically query loader.