implemented volume and pan effects

This commit implements a structure for sample processing and two implemenations
of this structure in volume and pan effects.

app/node/node.h

@@ -32,6 +32,7 @@
 #include "node/inputarray.h"
 #include "node/output.h"
 #include "node/value.h"
+#include "render/audioparams.h"
 
 /**
  * @brief A single processing unit that can be connected with others to create intricate processing systems
@@ -156,6 +157,16 @@ public:
    */
   virtual NodeInput* AcceleratedCodeIterativeInput() const;
 
+  /**
+   * @brief Return whether this node processes samples or not
+   */
+  virtual bool ProcessesSamples() const;
+
+  /**
+   * @brief If ProcessesSamples() is true, this is the function that will process them.
+   */
+  virtual void ProcessSamples(const NodeValueDatabase& values, const AudioRenderingParams& params, const float* input, float* output, int index) const;
+
   /**
    * @brief Returns the parameter with the specified ID (or nullptr if it doesn't exist)
    */