Adding testcase with multiple use of same stream, failing
Adding the possibility of tasks being functions.

This is required in order to use the same stream twice, as the Stream
object will be ended when one pipe is finished, and data sent from other
streams will just throw an error.
Updating doc to reflect new function possibility
Fixing indentation in example
Merge pull request #5 from bjornarg/multiple-streams

Reusable pipelines