Created and wired an implementation for the throttle operation on Observables.
Ensure static star imports are used for test cases.
No longer using Notification<T> for scheduling throttled events.
Cleaned up imports and removed unnecessary final keywords in the OperationThrottle class.
Fixed a typo the UnitTest class of OperationThrottle.
implemented count operator (#32)
added sum operations
added test against long sum, too (#83)
implemented average operation (#25)
implemented skipWhile and skipWhileWithIndex (#80)
added interval methods to Observable, where they were still missing
removed unused imports
Added the two variants of the first operator.
Added FirstOrDefault operation
Added link urls to the msdn descriptions
Merge pull request #354 from jmhofer/count-sum-average

Count, Sum, Average implementations
Merge pull request #355 from jmhofer/skip-while

implemented skipWhile and skipWhileWithIndex (#80)
Merge pull request #356 from jmhofer/interval

Added interval methods to Observable, where they were still missing
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