Fixes #43 by removing the Composer autoload requirement.
Add pull request template.
Use GitHub actions to run the CI tasks.
Update docs to start the "Usage" section with the required configuration for the plugin to do anything.
Switch to basic PHP includes for loading the PHP files instead of Composer autoload. We need to figure out the state of built files and the vendor directory before we can rely on Composer autoload.
Introduce helper methods for working with asset paths and URLs.
Fixes #34.
Fixes #43 by removing the Composer autoload requirement.