Remote file inclusion defence. We'll collect all possible API feature file names there. Later, when routing, if the file doesn't exist then boom, we don't include it.
$ : array
$api_feature_files : array
Constructor. Sets up arrays and finds API features
Returns the API features found
Returns the auth-free API features
Scans directories for API features in looking for plugins that are prefixed "api_feature_".
the path of the directory to be scanned