- Changed router so it supports both string and object as exception handlers.
- Added `Router::error($callback)` method to `Router` class (issue #238).
- Fixed issues calling `getController` and `getMethod` when callback is an object (issue #239).
- Updated documentation to reflect new changes.
- Added `addExceptionHandler` to `IGroupRoute` interface and `RouteGroup` class.
- Other minor bugfixes and optimisations.
