Add better date configuration support

Replace --since flag with --from and --to flags in order to have more
control over calculated date range.
Merge pull request #1 from grobie/better-date-support

Add better date configuration support
Remove duplicated slash in pagerduty API URLs
Fix office hour calculation

The first hour in the officehour range should be counted as well.
Fix location timezone conversion

This change loads a location object with proper summer/winter time
support instead of using a fixed GMT offset calculation.