Fixing CEP-922

WindowProcessor's restoreState() is called twice by passing two different parameters
Changing Siddhi version to 2.2.0
Committing the fix for https://wso2.org/jira/browse/CEP-951
Fixing time based issues in SnapshotOutputRateLimit test11
adding siddhi sample module
Merge pull request #18 from tishan89/master

adding siddhi sample module
Improving the performance test build
Fixing intermittent build failure in org.wso2.siddhi.test.standard.ratelimit.SnapshotOutputRateLimitTestCase.testSnapshotOutputRateLimitQuery7
Making Siddhi API Serializable