Automated wrapping for I32/U32 API parameters.
Wrap a bunch of Perl API functions/macros.

Adds sv_2nv, sv_2nv_flags, SvANY, SvNVX, SvFLAGS, SvNOK_nog:
all the building blocks required for SvNV.
Implement the inlined version of SvNV.

The speedup is very low (around 2% on a microbenchmark) compared
to the non-inlined version.