timelapse into RAM instead of HDD

[migod2]

Hi -

I'd like to propose timelapse_mode = 5m,10m,15m,30m (minutes) on top of hourly/daily etc.
I made necessary changes in recent code, and tested, but cannot commit.

Purpose: write files to ramdisk (tmpfs) and tranfer to hdd by cron job & shell script (avoid constant write to hdd)