Version 0.11.98

+ Implemented local configuration caching.
  Mostly implemented in LocalDB with interface in DB.
  Config caching doesn't have fixed update interval using session instead.
  Session start triggers cache update
  (this change was made in payments.Reader.begin_session).
+ Implemented FreeTime configuration value awareness for tariffs. Tariff constructor
  now accepts free_time argument - number of free minutes.
  This change affects unit calculation for ticket-related tariffs.
  NOTE: FreeTime awareness for Tickets is not included in this version
  (still 15 minutes constantly).
+ Moved doctests for FixedTariff and DynamicTariff into tariff_test module.
+ Fixed incorrect behavior during handling 'R' (reader) command response from terminals.
  Due to incorrect assumption, nonexistent cards weren't handled properly thus causing
  terminal communication to stall.