Operators Skip, SkipLast, Take with time
Manual Merge github.com:akarnokd/RxJava SkipTakeTimed2

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java
	rxjava-core/src/main/java/rx/operators/OperationTakeLast.java
Merge pull request #697 from benjchristensen/skip-take-time-merge

Manual Merge of Pull #667