More standard plugin header style. Remove legacy Automattic plugins link.
Rename WP_Client to Syndication_Client.

We should be good and prefix our classes and avoid breaking things by conflicting with future core code.
More prefixing across the plugin (using "Syndication_" as the prefix).

Remove need to multiple hard-coded references to class names structures across the push syndication server class.
Rename files to more appropriately reflect updated class names.