Unblock the accept thread on shutdown

Merge #120 a=@moises-silva r=@frewsxcv
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I'd like to find a better way, but, this works and is not completely awful, is it? :)

If this is not acceptable I'd like to initiate a discussion on ideas on how to handle shutdown correctly. Currently if tiny-http is used in a loadable module (I am using it inside a project that can load/unload modules from an interactive command line a system administrator controls), when the server goes out of scope the socket lingers because the thread never terminates unless there's a new tcp connection received (accept is a blocking call).

An alternative to this would be to put the socket in non-blocking mode and then somehow poll() or select() on it with a timeout to check every sec for the shutdown flag (close trigger bool).

I may be wrong, but I don't see many downsides to this implementation. The Drop() call *could* hang for a bit on unusual situations like the server being inaccessible to itself (e.g 127 -> 127 firewall blocking or whatever), but the connection will timeout and move on. Most cases are better off with this as far as I can tell.

Thoughts?

src/lib.rs

@@ -126,7 +126,7 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicBool;
 use std::thread;
 use std::net;
-use std::net::ToSocketAddrs;
+use std::net::{ToSocketAddrs, TcpStream, Shutdown};
 use std::time::Duration;
 use std::sync::atomic::Ordering::Relaxed;
 
@@ -300,7 +300,6 @@ impl Server {
                 let new_client = match server.accept() {
                     Ok((sock, _)) => {
                         use util::RefinedTcpStream;
-
                         let (read_closable, write_closable) = match ssl {
                             None => {
                                 RefinedTcpStream::new(sock)
@@ -413,5 +412,10 @@ impl<'a> Iterator for IncomingRequests<'a> {
 impl Drop for Server {
     fn drop(&mut self) {
         self.close.store(true, Relaxed);
+        // Connect briefly to ourselves to unblock the accept thread
+        let maybe_stream = TcpStream::connect(self.listening_addr);
+        if let Ok(stream) = maybe_stream {
+            let _ = stream.shutdown(Shutdown::Both);
+        }
     }
 }