Implemented basic timezone handling. Default zones can be set as context (EWSClient#set_time_zone) or override for start and end times. Implemented #get_time_zones to request all available time zones.
Initial support for tasks

Reintroduce tasks support with item creation in a tasks folder
Merge pull request #120 from sisutcliffe/tasks-support

Initial support for task creation
Merge pull request #119 from RmMsr/feature-time-zone

Feature: TimeZoneContext and GetServerTimeZones