Use Github-flavoured markdown in the whole website, including forum

Hi everyone, after our website maintainer’s effort, the whole website, including all news, wiki pages and forum posts have been converted to github flavoured markdown format, instead of the old textile format.

You can read this link for more details of markdown.

The most important thing is that, when you try to write a code block here, you can still use the old format, <pre></pre>, or use a new convenient format:

C++

```cpp
MyClass* var = new MyClass;
delete var; 
var = nullptr;
```

Then it will show like this on forum

MyClass* var = new MyClass;
delete var; 
var = nullptr;

JavaScript

```javascript
var TestClass = Base.extend({
    _var1:null,
    _var2:null,
    doSomething:function (number) {
        var size = director.getWinSize();
    }
});
```

Well, it shows like this:

var TestClass = Base.extend({
    _var1:null,
    _var2:null,
    doSomething:function (number) {
        var size = director.getWinSize();
    }
});

Lua

```lua
local function foo()
    local layer = cc.Layer.create();
    return layer;
end
```
local function foo()
    local layer = cc.Layer.create();
    return layer;
end

oops, lua will be support in the coming week :slight_smile:

This is great! Thank you!

python

for i in range(1,500):
    print "This is great news!"
print "Thank you"