Per method batch disabling

This is only a preview. Tests and more docs are forthcoming. I just wanted to get the other maintainers opinion on this interface.

The per-method batch disabling will be configured in the frontend and it's done through the Api class constructor like so:
```
var api = new Api('/api', {noBatchingForMethods: ['slow-poke']});

api.exec('ordinary-method', {boringParam: 'boring value'}); // this method will be batched

api.exec('slow-poke', {huh: 'uh?!'}); // this method won't be batched
```
Also, 
1. I think it's better to simply use `instanceof Array` checking. The drawback for this method that I know of is that an array that comes from another window, iframe etc is not recognized as an array.
2. If `instanceof Array` is not acceptable, I'd take a look at the [polyfill](https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray) for the `Array.isArray`.