Add support for deferred stop for graceful shutdown. (#153)

Author: ioquatix

lib/async/http/protocol/http1/server.rb

@@ -55,7 +55,7 @@ def each(task: Task.current)
 								return
 							end
 
-							begin
+							task.defer_stop do
 								# If a response was generated, send it:
 								if response
 									trailer = response.headers.trailer!

lib/async/http/protocol/http2/connection.rb

@@ -89,6 +89,7 @@ def read_in_background(parent: Task.current)
 
 							task.annotate("#{version} reading data for #{self.class}.")
 
+							# We don't need to defer stop here as this is already a transient task (ignores stop):
 							begin
 								while !self.closed?
 									self.consume_window

lib/async/http/protocol/http2/server.rb

@@ -53,7 +53,7 @@ def each(task: Task.current)
 
 							@count += 1
 
-							begin
+							task.defer_stop do
 								response = yield(request)
 							rescue
 								# We need to close the stream if the user code blows up while generating a response: