Prevent autoloading from loading already initialized objects

[szul]

If custom code is run first, auto-loading can then be prevented from running a second time if someone forgets to add data-m-autoload="false' to their HTML. This would then make the data-m-autoload attribute unnecessary.

[szul]

Could be accomplished with a metron.done() function that runs after all the “ready” code is complete. This would eliminate the explicit autoload attributes and the need to call init() on custom code.