nghttp2: new package

nghttp2 is an implementation of HTTP/2 and its header
compression algorithm HPACK in C.

Signed-off-by: Michaël Burtin <michael.burtin@netgem.com>
Signed-off-by: Anisse Astier <anisse.astier.ext@netgem.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>