Corrections to author attribution and other header information.
Fixed typo in license warning message.
Updated readme information to match php file header.
Changed attribution URL from author/site to indivudal content, to match
how the license is generated officially.
Removed author info from non-singular listing pages, since it most often is nonsensical.
Added license to the plugin header and license.txt

I forgot to include the license. It's included now :)
Added extra info & screenshots for v2 release

I've added two screenshots of what the plugin does in the admin
interface and updated the readme with some extra info on the plugin's
license and some info on how to contribute.
Screenshots added