Pass config to `new Comb()` and make it chainable (#102)

Issue #102

You can now create new Comb instance and configure it at the same time.
To use one of predefined configs, pass its name:

```js
var comb = new Comb('zen'); // or `csscomb`, or `yandex`
```

To use custom config, pass its object:

```js
 var comb = new Comb({ 'always-semicolon': true });
```

Also `new Comb()` and `configure()` are chainable now.
It means you can do things like:

```js
// Init, configure and process:
var combed = new Comb('csscomb').processString('a { color: tomato }');

// Comb a file with one line of code:
new Comb().configure({ 'always-semicolon': true }).processFile('panda.less');
```