Revert use of autoload

[jcs]

Hi, I'm using this module on OpenBSD in an environment that uses its pledge mechanism to restrict the functionality of the program for increased security when parsing untrusted images.

The 0.4.0 release of gd2-ffij changed the behavior to autoload classes at runtime, which breaks my application because it's not allowed to read additional files once pledge has been called. The previous release used require so the entirety of the gd2-ffij module was loaded by the time my application called pledge to lock things down.

Could this use of autoload be reverted to go back to require each dependency up front?