Updating RSVP status when a reply comes in.

Hopefully this fixes @DominikTo's bouncing event issue.
Typo
added getScheduleStatus() method
updated changelog
Merge pull request #118 from DominikTo/get-schedule-status

added getScheduleStatus() method
Support for detecting significant changes in iTip objects.

Fixes #119
PHP 5.3
Support for SCHEDULE-FORCE-SEND

Fixes #120.
When a parameter value contains +, quote the value.
Updated changelog.
Don't generate REPLY messages for events that have been CANCELLED.

Fixes #122
thnx @dominikTo
SUMMARY in scheduling messages. #123
using getValue()
updated changelog
Merge pull request #124 from fruux/itip-summary

SUMMARY in scheduling messages. #123
scheduleStatus() returns just the status code
We're validating RELATED but it should have been RELATED-TO.

Fixes #130
Merge branch '3.3' of github.com:fruux/sabre-vobject into 3.3

Conflicts:
	ChangeLog.md
ATTACH is a URI value, unless it's specified as BINARY. We had it the other way around.

Fixes #128