Bring in libnv library for managing name/value pairs. The following types
are currently supported:

- NV_TYPE_NULL - only name, no data;
- NV_TYPE_BOOL - boolean (true or false);
- NV_TYPE_NUMBER - 64bit unsigned integer;
- NV_TYPE_STRING - C string;
- NV_TYPE_NVLIST - nested nvlist;
- NV_TYPE_DESCRIPTOR - file descriptor;
- NV_TYPE_BINARY - binary data.

For detailed documentation and examples see nv(3) manual page.

Sponsored by:	The FreeBSD Foundation