[WIP] ProcessorBase multi-threading

[WIP] Depends on !89 (merged) .

Add a ThreadedBaseClass that ProcessorBase inherit from.

It allows the computation of the ProcessorBase::process(...) to be performed in a separated thread. Threads aren't instantiated/killed but instead are put to sleep waiting for new CaptureBase.

ThreadedBaseClass API is rather simple :

• Constructor with argument max_frequency allowing the user to set guess what, a max frequency at which the processor operates.
• run() to start the thread and so the processor.
• stop() allows to stop the thread and so the processor.
• isRunning() let the user know if the processor is running or not.

Finally it has the pure virtual function :

• executeImpl() where the derived class do its job.

src/processor_motion.h

@@ -202,7 +202,7 @@ class ProcessorMotion : public ProcessorBase
          *   - initializing counters, flags, or any derived variables
          *   - initializing algorithms needed for processing the derived data
          */
-        virtual void preProcess() { };
+        virtual void preProcess() { }
 
         /** Post-process
          *
@@ -214,7 +214,7 @@ class ProcessorMotion : public ProcessorBase
          *   - resetting and/or clearing variables and/or algorithms at the end of processing
          *   - drawing / printing / logging the results of the processing
          */
-        virtual void postProcess() { };
+        virtual void postProcess() { }
 
 
         // These are the pure virtual functions doing the mathematics