MobyGames API no longer free

[Senyksia]

Sometime in the past week (AFAICT) the MobyGames API has been moved to their MobyPro subscription, and their documentation has removed mention of the previous method to obtain a key. I'm unsure how this affects existing keys, but I presume they are free for life.

The paid offering isn't an issue, but it does mean that the Steam API is the only free extensive game source available to the plugin now.

Currently the only fix needed is updating README.md and the API description to reflect the change. Assuming the change is permanent, then in future another API for games may be beneficial.