HTTP/2: removed http2_idle_timeout and http2_max_requests. Instead, keepalive_timeout and keepalive_requests are now used. This is expected to simplify HTTP/2 code and usage. This also matches directives used by upstream module for all protocols. In case of default settings, this effectively changes maximum number of requests per connection from 1000 to 100. This looks acceptable, especially given that HTTP/2 code now properly supports lingering close. Further, this changes default keepalive timeout in HTTP/2 from 300 seconds to 75 seconds. This also looks acceptable, and larger than PING interval used by Firefox (network.http.spdy.ping-threshold defaults to 58s), the only browser to use PINGs.