Support to close idle connections in HTTP/TCP clients/servers after a co...

...nfigurable timeout
I'm afraid that using ChannelInboundHandler instead of ChannelDuplexHandler will only consider inbound messages to the netty handler (that corresponds, in this case, to writing to the socket). The idea is to consider inactivity for both reading/writing. So, if we have a very slow server, that replies after 5 minutes, it makes a difference to consider innactivity in both directions.
I don't know if it's "expensive" to maintain ChannelDuplexHandler. If expesive, we can use ChannelInboundHandler because it is a reasonable simplification.

I agree with you that we should make Sharable the closeIdle handler (the idle handler cannot be shared because the idleTimeout is configurable and might change).