Bugfix - Upgrading HTTP error handling

## HTTP error handling

This PR updates Paulus to use the newer style of HTTP error handling introduced in chriso/klein.php#16.

This is especially important since the old style of HTTP error handling has been deprecated as of chriso/klein.php#221.

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### Composer bits

This PR also cleans up some of the composer requirements since PHP Codesniffer was yelling at me for a false-positive PSR-2 compliance issue. When I went to upgrade it, I figured I'd clean up the composer requirements to use the newly suggested style of version constraints.

This new style of version constraints is not only suggested, its now the automatic designation as of composer/composer#3096. More info on and explanation of this new suggestion can be found here:
http://blog.doh.ms/2014/10/13/installing-composer-packages/
Do you want to include the `@throws` tags here?