Timeouts should be optional

[edsko]

(This is a companion issue to kazu-yamamoto/http2#112).

Although we can override the timeout through Settings.settingsTimeout, we cannot disable such timeouts. For the reason explained in the http2 issue, working around this limitation by simply choosing a really high value is only possible on 64-bit machines.

[kazu-yamamoto]

You can modify both libraries as you like.