Power-down mode was implemented as a delay instead of calling sleep_sec. Also, force GPS power-down with a cpu power-down, otherwise updates from GPS would wake cpu because of pin change interrupts used by SoftwareSerial. Prevent GPS power down when it has no fix. Changed sleep_sec to accept a uint16_t.
|GPSconfig.h||split .h file out|
|SD_GPSLogger.pde||Fixed power-down mode|