Introduce new naming convention for class files

[lukecarbis]

Issue #448 Introduces a new file naming convention for the file containing the WP_Stream_Author class. As @westonruter points out, this is inline with the file naming convention in WordPress core.

Any files dedicated to a single class should adopt the filename format of:
class-dash-separated-class-name.php

For example, settings.php which contains the class WP_Stream_Settings should be renamed to class-wp-stream-settings.php.

This is also a good opportunity to explore whether or not it would be helpful to split the includes folder into an includes and a classes folder.

[westonruter]

Also would be nice to use this as an opportunity to implement autoloading, so that we can kiss require_once( 'classes/...' ) goodbye.

[lukecarbis]

We'll see this in 2.0.0.