markdown syntax highlight in markdown code example

Example 1: markdown code snippet

```javascript
var s = "JavaScript syntax highlighting";
alert(s);
```
 
```python
s = "Python syntax highlighting"
print s
```
 
```
No language indicated, so no syntax highlighting. 
But let's throw in a tag.
```

Example 2: code highlight in readme

```js
function myFunction () {
   return 42;
}
```