Add 2h keepalive by default

[jq-rs]

trafficstars

Add 2h keepalive by default to drop unused TCP sessions (e.g. behind a firewall).

Fix unused deprecation error given by new compilers.

[jq-rs]

Fixes #854. New 0.1.x release is kindly requested if this PR is approved.

[jxs]

Hi, and thanks for the PR. I wonder if we should also allow for the user to configure it via Server. CC @seanmonstar

[jq-rs]

If the 2 h default is not acceptable, I can certainly implement an API, please do suggest what kind of API would be preferable. To me, this feature itself is a must-have for public internet web servers.

[jxs]

if you are on a rush, you can convert your warp filters to Service and set the keepalive on hyper

[jq-rs]

Configurable solution available in #1075, closing this.