External poll support generates a lot of messages on a busy system
for no value unless you're one of the few people using it. It's
not recommended for new users and is there for backwards compatibility.
Make it not built by default and selectable by cmake option.
Generic sessions has been overdue some love to align it with
the progress in the rest of lws.
1) Strict Content Security Policy
2) http2 compatibility
3) fixes and additions for use in a separate process via unix domain socket
4) work on ws and http proxying in lws
5) add minimal example
