Fix slow exchanges on linux by adding polling and other improvements (#14)

* add prints to investigate slowness

* add loop sleep for blocking Stack

* add connection close http attribute and detect end of HTML page

* add timeout to bridge read

* examples/xnet: add ntp timestamp to prints and show output in readme

* add polling to http tap interface

* more digits in ntp format

* prevent crashes on non-8 timestamp

x/xnet/stack-retrying.go

@@ -8,9 +8,9 @@ import (
 	"github.com/soypat/lneto/tcp"
 )
 
-func (s *StackAsync) StackRetrying() StackRetrying {
+func (s *StackAsync) StackRetrying(loopSleep time.Duration) StackRetrying {
 	return StackRetrying{
-		block: s.StackBlocking(),
+		block: s.StackBlocking(loopSleep),
 	}
 }