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...`.

This is not allowed by phpunit as a test may not fail anymore

- better throw http exception on not satisfiable range request
- constitent header names
- fixed range end when range request is to the end
- added unit test

related to #275, fixes #148