Adds CODING_STYLE.md and RELEASE_NOTES files

The files are also added in the Xcode project

CODING_STYLE.md

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+# cocos2d-x C++ coding sytle
+
+
+## Detailed information
+
+Please, refer to this document for a detailed version of the cocos2d-x C++ coding sytle:
+
+* [cocos2d-x c++ coding style](http://www.cocos2d-x.org/wiki/Cocos2d_c++_coding_style)
+
+
+## Quick Sample
+
+Use this sample as a quick reference. But DO READ the detailed doc for more info.
+
+Header file:
+
+```c++
+/** 
+ * We use Doxygen strings for documentation.
+ * All public classes, methods, structs should be documented using Doxygen Strings
+ */
+class CC_DLL Sprite : public NodeRGBA, public TextureProtocol
+{         /* class braces start in a new line */
+
+/* no indentation here  for public, protected or private */
+/* First add all the "public" stuff, then all the "protected" stuff, and finally all the "private" stuff
+public:   
+
+    /* we don't use tabs, we use spaces, and we use a 4 space identation */
+    /* 1st add all static const */
+    static const int INDEX_NOT_INITIALIZED = -1; 
+
+    /* then add all the creators and other relevant static methods */    
+    static Sprite* create();    
+    static Sprite* create(const char *filename);    
+    static Sprite* create(const char *filename, const Rect& rect);
+
+    /* if applicable, then add the consturctors / destructors */        
+    Sprite();    
+    virtual ~Sprite(void);
+
+	/* then add all the initialization methods */    
+    /* notice that they are in the same order as the creators */
+    virtual bool init(void);    
+    virtual bool initWithTexture(Texture2D *texture);    
+    virtual bool initWithTexture(Texture2D *texture, const Rect& rect);
+    
+    
+
+    /* then add the regular instace methods */
+    virtual void updateTransform(void);    
+    virtual SpriteBatchNode* getBatchNode(void);
+    virtual void setBatchNode(SpriteBatchNode *spriteBatchNode);
+     
+
+    /* then add all the overriden methods */
+    /* notice that all overriden methods must use the 'override' keyword */
+    /* overriden methods are not forced to have doxygen strings UNLESS they change the behavior in a non obvios way */
+    virtual void setPosition(const Point& pos) override;
+    virtual void setRotation(float rotation) override;
+    virtual void setRotationX(float rotationX) override;
+
+    
+	/* once you finish with the 'public' methods, start with the 'protected' ones */
+protected:
+
+    /* protected methods are not forced to have Doxygen strings, but if they have it, better */
+    void updateColor(void);
+    virtual void setTextureCoords(Rect rect);
+
+    /* After adding all the methods, add the ivars */
+    /* all ivars must start with _ */
+    /* Do not use Hungarian notation */
+    TextureAtlas*       _textureAtlas;      /// SpriteBatchNode texture atlas (weak reference)
+    int                 _atlasIndex;        /// Absolute (real) Index on the SpriteSheet
+    SpriteBatchNode*    _batchNode;         /// Used batch node (weak reference)
+};
+
+```
+
+Implementation file:
+
+```c++
+/* Do not use doxygen comments on the implementation file */
+
+/* The methos MUST be in the same order as where declared in the header file */
+
+Sprite* Sprite::create(const char *filename)
+{
+	/* Don't use tabs. Use spaces. Use 4-space indentation */
+    Sprite *sprite = new Sprite();
+
+	/* put curly braces in the same line as in the 'if'*/
+	/* leave a space between the 'if' and the '(' */
+	/* don't leave spaces between '()' */
+    if (sprite && sprite->initWithFile(filename)) {   
+        sprite->autorelease();
+        return sprite;
+    }
+    CC_SAFE_DELETE(sprite);
+    return NULL;
+}
+
+/* Initialization list can be indented to 0 spaces, or to 4 spaces. If in doubt, be consistent with the indentation already used in the file */
+/* Only use the Initialization lists for types that can't fail when initialized */
+Sprite::Sprite()
+: _shouldBeHidden(false)
+, _texture(nullptr)
+, _physicsBody(nullptr)
+{
+}
+
+/* use the 'initXXX' methods to initialize types that might fail */
+bool Sprite::initWithTexture(Texture2D *texture, const Rect& rect, bool rotated)
+{
+    /* it ok not use use curly braces */
+    if (something)
+    	do_something();
+    else
+    	something_else();
+
+    /* but if you use curly branches in one branch, all the branches should use curly branches */
+    if (something) {
+    	do_something1();
+    	do_something2();
+    } else {
+    	so_something_else();
+    }
+}
+
+```

RELEASE_NOTES

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+===== cocos2d-x 3.0 Release Notes =====
+
+Please, read the online release notes document:
+http://www.cocos2d-x.org/wiki/Release_Notes_for_Cocos2d-x_v300