Add 'BEM' preset

closes #30 
Так норм?

```js
var A = function () {};
var B = function () {}; 

B.prototype.log = function () { console.log('B'); }; 
A.prototype = B.prototype; 
A.prototype = new A();

var a = new A(); 
var b = new B();

a.log(); // 'B'
b.bla(); // TypeError: B.bla is not a function
```