Introduce a clear distinction between internal exceptions and
user-visible exceptions, leaving AFPException as base abstract class.
Later, it should be possible to narrow some types around, e.g. in
ParserStatus (that might work with user-visible exceptions only).
Also a future TODO is putting all the exceptions in their own namespace
(probably ...\Parser\Exception).
Change-Id: I4e33a45117f0a3e73af03cc1e3f2734beaf2b5e1
