Extract an interface from Option<T>
Extract an interface from Stream<T>
Extract an interface from Either<TLeft, TRight>
Extract an interface from Reply<TToken, TResult>
Extract an interface from Future<T>
Modify the signature of Parser<TToken, TResult>, make TOutput covariance
Modify the signature of Cps<TResult, T>, make T covariance
Move extension methods
Fix the definition of Cps<TResult, T> for Silverlight
Merge pull request #8 from takeshik/interfaces

Extract interfaces and introduce covariance