Stereo camera function is integrated.

I integrated stereo camera support to Camera class without changing any usage. The only method that should be called to switch to stereo camera mode is setStereoCamera method. When the stereo mode is active, all editable parameters such as Format7, Bayer ...etc is adjusted in setup(). Otherwise, the usage of library is exactly the same as the old. Basically, I overrided the grabVideo and grabStill methods to grab stereo frames. 

Unfortunately, I had only the opportunity to test with Bumblebee2 that I only have. It has limited features for stereo capture, because I could not take into account more use cases. Now, it can perfectly de-interlace stereo frames and convert them into RGB images. 

The simplest example in stereo mode looks like:

```c++
#include "ofxLibdc.h"

class testApp : public ofBaseApp {
public:
    ofxLibdc::Camera camera;
    ofImage frame1;
    ofImage frame2;

    void setup() {
        camera.setStereoCamera(true);
        camera.setup();
    }

    void update() {
        if (camera.grabVideo(frame1, frame2)) {
            frame1.update();
            frame2.update();
        }
    }

    void draw() {
        frame1.draw(0, 0);
        frame2.draw(camera.getWidth(), 0);
    }
};
```