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
Create README.md
Update README.md
Update README.md
Observable.from: refactor varargs to overloads

https://github.com/Netflix/RxJava/issues/359 Varargs cause compiler warnings
Observable.concat: refactor varargs to overloads

https://github.com/Netflix/RxJava/issues/359 Varargs cause compiler warnings

As part of this I also changed this:

```java
public static <T> Observable<T> concat(Observable<Observable<? extends T>> observables)
```

to

```java
public static <T> Observable<T> concat(Observable<Observable<T>> observables)
```

I documented the reasoning of this at https://github.com/Netflix/RxJava/issues/360#issuecomment-24121217
Observable.merge: refactor varargs to overloads

https://github.com/Netflix/RxJava/issues/359 Varargs cause compiler warnings
Observable.startWith: refactor varargs to overloads

https://github.com/Netflix/RxJava/issues/359 Varargs cause compiler warnings