[FLINK-1282] [docs] Update layout of docs

This closes #235.
[FLINK-1286] [APIs] [runtime] Fix serialization in CollectionInputFormat and generate meaningful error messages
[FLINK-1278] [runtime] (part 1) Remove special code paths for the Record data type in the input readers and the source task.
[Scala API] Case Class serializer can work with classes that cannot be instantiated empty