[FLINK-933] Add primitive input format to read a sequence of primitives

This closes #47
[FLINK-993] Primitive input format fails for invalid input. Adapted documentation.
[streaming] Source parallelism API update

The new preferred way is calling setParallelism() after adding the SourceFounction. This solution works any other operator.
[streaming] Fixed async buffer sending at end of AbstractInvokable