interface to the best available JSON module

 JSON::MaybeXS first checks to see if either Cpanel::JSON::XS or JSON::XS is
 already loaded, in which case it uses that module. Otherwise it tries to load
 Cpanel::JSON::XS, then JSON::XS, then JSON::PP in order, and either uses the
 first module it finds or throws an error.
 .
 It then exports the encode_json and decode_json functions from the loaded
 module, along with a JSON constant that returns the class name for calling
 new on.