Finished the injector API. This system is similar to the expansion API in terms of how you use it. A server owner would simply drop the injector he / she wants to use in the PlaceholderAPI/injectors/ folder.
These injector modules may have configuration options that are added to the PlaceholderAPI.config.yml file.like so:
After first load of an injector with config options, simply edit the options to the values you want, then use /papi reload to update your injector settings.