Streaming-support integrated in Accelerate base package.

Streaming-support in CUDA backend is in another pull request. 
We picked lists because it was the most general structure that could be used by other streaming IO frameworks (like pipes or conduits). 

It does make it difficult if you want to stream in scalars. This issue could probably be solved in part by something like

```haskell
subdivide :: slix -> Seq [Array (FullShape sl) a] -> Seq [Array (SliceShape sl) a]
```

This would allow the user to stream in a list of larger arrays and split them up into a sequence of scalars (or any other smaller array size) without going via a list. It would basically be like the `toSeq` operation, but would work on the whole stream.