Extend docs with supported status returns. Add several helper functions
which allow to check the particular status.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Define base `Status` interface. Provide the functionality to distinguish
success and failure returns. Provide functionality to transport statuses
over NeoFS API V2 protocol. Support success `OK` and failure `INTERNAL`
returns.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>