Added support for different response formats.
Support for error response in different formats.

use `getIs...` instead of `is...` to allow these methods to be used as
virtual properties.

This is forconsistency to the rest of the framework.
Only methods that take parameters may be named `is...`.

issue #303
Here is the proposal for RESTful routing syntax:
https://gist.github.com/cebe/5674918

It allows to filter actions by HTTP request methods