Add chainability to bh.match

It allows to use familiar and convenient pattern.
Instead of:
```js
module.exports = function(bh) {
    bh.match('block', ....);
    bh.match('block__elem1', ....);
    bh.match('block__elem2', ....);
};
```
We can write:
```js
module.exports = function(bh) {
    bh
        .match('block', ....)
        .match('block__elem1', ....)
        .match('block__elem2', ....);
};
```