feat(presets): add `two-dashes` preset
feat(presets): add `two-dashes` preset

This preset create naming by Harry Roberts.

It is nessesary to not pass all options every time you use the
convention by Harry Roberts.

```js
var bemNaming = require('bem-naming');

// without preset
var myNaming = bemNaming({
    elem: '__',
    mod: { name: '—-', val: '_' }
});

// with preset
var myNaming = bemNaming('two-dashes');
```

bem/bem-naming,bem-sdk/bem-naming