===== FastFlow (simple) pipeline =====

First of all, 
<code>
#include <ff/pipeline.hpp>
</code> and possibly
<code>
using namespace ff;
</code>

Pipelines may be created creating an **ff_pipeline** object: 
<code>
ff_pipeline myPipe;
</code>

Stages may be added using the **add_stage(ff_node*)** (in order).
<code> 
myPipe.add_stage(stage1); 
myPipe.add_stage(stage2);
</code>

A pipeline with all the stages added may be run by invoking the **run_and_wait_end()** method:
<code>
myPipe.run_and_wait_end();
</code>

Each stage returns:
  * a pointer to a task (in case it wants to pass a result)
  * a NULL pointer (in case it wants to terminate)
  * a GO_ON constant (in case it does not terminate but wants to go waiting for a new task without actually delivering a result)
The values may returned with a **return** or (in any part of the code) via a **ff_send_out(...)** call (may be called multiple times in a stage)