Count-properties rule

@stubbornella

This is a new rule for counting properties and pair-values in the CSS. It export and object.

usage : 
```javascript
var result = CSSLint.verify(".foo { float: left; }", { "count-properties": 1});
console.log(result.stats['count-properties'].properties.float.count;)
```
*Output* : 1

```javascript
var result = CSSLint.verify(".foo { float: left; }", { "count-properties": 1});
console.log(result.stats['count-properties'].stringResult);
```
*Output* : {"float":{"count":1,"values":{"left":{"count":1}}}}