Composer support.

This adds a `composer.json` file to the module, so that it can be installed via [Composer](https://getcomposer.org/).

I was unable to load the Cyntax Open Technology License referenced [here](http://code.cyntaxtech.com/modules/kohana-settings/license) (the [link](http://code.cyntaxtech.com/licenses/cyntax-open-technology) is dead), so put the Kohana default in (BSD-3-Clause). What is the correct licence?