Return nil for nil input
Remove liinefeeds
Avoid occuping database too match

Extraction of one hour of events takes about 10 seconds
ruby scratch/create_markers.rb 12:00:00 13:00:00 ~/var/locations.sqlite ~/var/events.sqlite

Extracting events from 2013-04-23 22:00:00 UTC to 2013-04-23 23:00:00 UTC