libvici currently relies on libstrongswan, and therefore is bound to the GPLv2.
But to allow alternatively licensed reimplementations without copyleft based
on the same interface, we liberate the header.
As we want to avoid the libstrongswan include dependencies for libvici, avoid
the use of the bool type. Unfortunately this change may break the ABI for
vici_dump(). As this function is mostly for debugging purposes, we do it
nonetheless; my apologies if somebody already relies on the ABI stability of
that function.