get_npn_protocols() is high level wrapper for
spdylay_npn_get_proto_list() and the returned list can be passed to
ssl.SSLContext.set_npn_protocols().

spdylay_npn_get_proto_list() returns a pointer to the supported SPDY
version list. The element of the list is spdylay_npn_proto struct. It
contains all SPDY version information this library supports. The
application can use this information to configure NPN protocol
offerings/selection.

ssl socket and ssctrl are also instance variable now.

Patch from Stephen Ludin