Fixed time skew bug

Using multiple RaspiStill commands to get streaming frames, results in lower streaming frame rate but more accurate timelapse delays.
Update stop_timelapse.sh
Update PI_SETUP.md
Update start_timelapse.sh
Updated start timelapse script
Merge branch 'time-fix' of https://github.com/DanNixon/FP_StreamTimelapse into time-fix
Merge pull request #8 from DanNixon/time-fix

Fix time skew bug