[WIP] - Throwing exceptions

[JeroenSormani]

Wanted to do a proposal to allow for throwing Exceptions during form validation. The current PR as is doesn't include this, but I'd even like to take it a step further and also include the form/action processing in the try/catch so Exceptions can also be thrown during processing Actions.

Throwing a Exception would be a easier way of capturing errors and easier for a custom error (message) to be added.

I've come to this PR by wanting to have a way to have configurable validation rules while processing a form (checking a support license through API for example). Being able to create a custom License Validation Action where maybe I add message setting for example or API key for the call it needs to do.

Let me know what you think about using Exceptions in such manner..

[JeroenSormani]

PS. this won't change existing validation configurations to prevent some small change of breaking existing customizations users may've done.

The following example shows what could break if a user has a custom way of throwing a exception and is not accounting for that in a hook with the current way of things.

add_action( 'hf_form_error', function( $error_code, $form, $data ) {

	error_log( 'The following error occurred: ' . $error_code ); // Works, message only
	update_post_meta( $form->ID, '_last_error', $error_code ); // Works, but maybe unexpectedly for the one to see a Exception stored
	update_option( 'test', $error_code ); // Breaks! Trying to clone a uncloneable object

	if ( ! empty( $error_code ) || $error_code == 'test' ) { // No errors

	}

}, 10, 3 );