Allow getting many items at once
Parse deleted occurrences
Parse correctly the responses
Add support for modified events
Parse item attachements
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.
Some test clean-up
Merge branch 'master' of https://github.com/ifad/Viewpoint into ifad-master

Conflicts:
	spec/unit/soap/builders/ews_builder_spec.rb