Avoid leaking goroutines on close

[liggitt]

Fixes #92

• Avoids leaking timers in shutdown and Wait if the functions exit before the timeouts expire
• Shortens the timeout for an unhandled error from 10 minutes to 1 second. It looks like the 10 minute timeout was added in calling conn close before stream close results in a soft deadlock #24 / Update close to not block on shutdown #25 without a rationale... happy to adjust this PR if there are other things aspects to consider. The paths where errors could be handled are:
  1. client calls CloseWait(). We know Close() is immediately followed by Wait(), a second seems entirely sufficient.
  2. client calls Close() followed by Wait(). We don't control the calls, but the expectation is that Close() is immediately followed by Wait(), so a second seems entirely sufficient.
  3. client calls NotifyClose(), GOAWAYFRAME notifies lastStreamChan, client responds by calling Wait(). lastStreamChan is notified before the shutdown is begun, which gives the caller a second to call Wait() if they want to handle the shutdown error. This is the only path I don't have a great intuition of, but a second to process the channel notification seems reasonable. I also can't find a single use of this function in a public github search.

[liggitt]

cc @dims @aojea

[dims]

LGTM

[dims]

@thaJeztah ok to merge and cut a tag with this change?

[thaJeztah]

Fine with me, but I'm not deeply familiar, so if you need more eyes, perhaps @dmcgowan can have a quick peek (otherwise feel free to move ahead)

[dims]

thanks @dmcgowan