MTK enhancements:

MTK enhancements:

 * Fixet fallback read size to 2000kB instead of 1984kB,
  mtk_logger will probe for max log size.
 * Somewhat experimental fix for parsing data after logger
  overwrite has occured. In this case the bitmask is overwritten/corrupted
  and we read it from block #2 instead.
 * A few extra precautions for Holux GR245.
 * Detect 'missing/zero block' - no action so far...

New features:
 * New option: log_enable (BOOL). This will 'Enable logging after download'.
  Use it if you have interrupted the download and the log has been
  disabled. By default logging is disabled during download and then
  re-enabled again (if previously enabled) - this will force log enable.
 * Partial log download - compare 'data.bin' and device log - start downloading
 * data at 'last unread block'. If device has been erased
 data.bin is moved to data_old.bin