gnurl: Import from wip (packaged by ng0)

libgnurl is a fork of libcurl. The goal for libgnurl is to support
only HTTP and HTTPS (and only HTTP 1.x) with a single crypto backend
(GnuTLS) to ensure a small footprint and uniform experience for
developers regardless of how libcurl was compiled.
This software is mainly used by GNUnet. The modifications to curl
are kept to the bare minimum, intended to track upstream closely.
gnurl is not a replacement for curl, so different paths are used.

(gdt)