Add both prefix and postfix versions of the increment/decrement
operators, and a static constexpr min/max which returns the
minimum/maximumm values that can be stored in the QSpecialInteger. These
latter functions are useful to define constants, e.g.:
typedef quint8_be IPv4_TTL;
static constexpr TTL_TO_DROP = IPv4_TTL::min();
Change-Id: I825a279feb68b93572765a9fdb5aa7b06d1be35b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>