Several bugfixes and enhancements

Hi,

While creating a demo app I found that GET methods like Customers.list didn't honor params (like limit:1). Sam e on iOS and Android.

Also, on iOS numeric params were not supported (limit:1 vs limit:"1").

And I've added Customers.update because I needed it for the demo app. I think it was not added by mistake because the other JS objects do have the update method.

Cheers,
Eddy