Reimplement the 'SequenceEqual' operator

Hi, this PR reimplemented the `SequenceEqual` operator #76 and should fix the issue #564.

The wiki page https://github.com/Netflix/RxJava/wiki/Observable-Utility-Operators#sequenceequal still needs to be updated. @DavidMGross could you help update the marble diagram of `SequenceEqual`? Thanks!