MINIFICPP-654 - C API: failure callback improvements

[arpadboda]

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[arpadboda]

It's not final, further changes expected as I'm not yet satisfied with the code quality, but the concept can be reviewed at least.

[phrocker]

@arpadboda is this ready for review? You stated, "it's not final"

[arpadboda]

Yes, I plan some further changes, but most probably in scope of a different PR.

[phrocker]

Do you think AS_IS could be clarified in the scope of the enumeration to better indicate the intent?

[arpadboda]

I agree with you that it's not the best naming as doesn't properly describe what happens, but no better idea. @apiri - you are our last hope. :)

[phrocker]

Looks good. minor comments, nothing that's a big deal...might want to resolve the misspelling, though.