micro-http: explicit HUP/ERR handling in server

The server in `micro_http` was not explicitly handling the `EPOLLHUP`,
`EPOLLRDHUP` and `EPOLLERR` epoll events. Added new checks that close
a connection that is signaled with these events.

Signed-off-by: George Pisaltu <gpl@amazon.com>
Signed-off-by: YUAN LYU <lyuyuan92@gmail.com>

src/connection.rs

@@ -428,7 +428,8 @@ impl<T: Read + Write> HttpConnection<T> {
         Ok(())
     }
 
-    fn clear_write_buffer(&mut self) {
+    /// Discards all pending writes from the connection.
+    pub fn clear_write_buffer(&mut self) {
         self.response_queue.clear();
         self.response_buffer.take();
     }