[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/examples/test_image.cpp

@@ -151,7 +151,8 @@ int main(int argc, char** argv)
// Preferred method with factory objects:
image_ptr = new CaptureImage(t, camera_ptr, frame[f % buffer_size]);
-        image_ptr->process();
+        //image_ptr->process();
+        camera_ptr->addCapture(image_ptr);
//cv::imshow("test",frame[f % buffer_size]);
std::cout << "Time: " << ((double) clock() - t1) / CLOCKS_PER_SEC << "s" << std::endl;
cv::waitKey(5);