Should close() wait for the server to shutdown?

[jgallagher]

Lifting this from a PR comment so it isn't lost now that the PR is merged without addressing this:

@smklein
After #537, I wonder if we should no longer make close wait for the server to terminate.

We could add a convenience close_and_wait for anyone that wants backwards compatibility?

@jgallagher
Changing the behavior of close() seems a little dicey from a backwards compatibility standpoint, but I do see your point. A couple other ideas, although I'm not sure I like these all that much more:

1. Deprecate close() and add two new methods: close_and_wait() + close_nowait().
2. Change close() to take an argument specifying whether or not to wait: close(CloseBehavior::Wait) or somesuch. This would be backwards incompatible in a way that old clients would have to update instead of silently getting different behavior.