n language wrapper support functions

In addition to the functions described in section 12.4.4.2, there is a family of functions that is used for automatic generation of wrapper functions, for example using the Prolog library library(qpforeign) that provides a Quintus/SICStus compatible foreign language interface.

The PL_cvt_i_*() family of functions is suitable for use with a _Generic selector or C++ overloading.^{220_Generic needs to take into account that there's no bool type in C but there is in C++. An overloaded integer() method is provided in the C++ interface.}

Note that the documentation on this API is incomplete. Also note that many of these functions are equivalent to the PL_get_*_ex() functions described in section 12.4.7.

int PL_cvt_i_bool(term_t p, int *c)

Equivalent to PL_get_bool_ex(). Note that the