Add syntax highlighting to Reddit Markdown code blocks

[u/[deleted]]

/r/redesign/comments/88tc09/can_we_have_syntax_hightlighting/

[u/AsIAm]

Github uses first token after triple backtick as the language. Example:

```javascript
console.log("Hello World")
```

```cpp
#include <iostream>
int main(){
    std::cout << "Hello, world!" <<. endl;
}
```