work_day_start default

Won't `work_day_start = 0` result in messed up times on the Sunday after a DST switchover if `work_day_start` isn't specified as past 2 in the query string? (I think... I might be confused)
Make sure we're looking at the start of the correct day.

Also updated the readme a bit
Merge pull request #13 from umts/dst

work_day_start default