Safer RsGxsChannel API

Deprecated old method which exposed interna async mechanism to the API
  users, making their and out life difficult
Things that really need to be async like turtle search/requests now accept
  callbacks, so the caller can be notified everytime some result is got
  back
Implement RsThread::async commodity wrapper to execute blocking API
  calls without blocking the caller, this could be optimized
  trasparently using a thread pool if necessary
Added hints into some retroshare-gui files on how to use RsThread::async
  thoghether with QMetaObject::invokeMethod and blocking RetroShare API
  to simplyfy interaction between GUI and libretroshare

libretroshare/src/util/rsthreads.h

@@ -27,6 +27,8 @@
 #include <iostream>
 #include <unistd.h>
 #include <semaphore.h>
+#include <thread>
+#include <functional>
 
 #include <util/rsmemory.h>
 #include "util/rstime.h"
@@ -239,7 +241,7 @@ pthread_t  createThread(RsThread &thread);
 
 class RsThread
 {
-    public:
+public:
     RsThread();
     virtual ~RsThread() {}
 
@@ -259,6 +261,17 @@ class RsThread
 
     void ask_for_stop();
 
+	/**
+	 * Execute given function on another thread without blocking the caller
+	 * execution.
+	 * This can be generalized with variadic template, ATM it is enough to wrap
+	 *	any kind of function call or job into a lamba which get no paramethers
+	 *	and return nothing but can capture
+	 * This can be easly optimized later by using a thread pool
+	 */
+	static void async(const std::function<void()>& fn)
+	{ std::thread(fn).detach(); }
+
 protected:
     virtual void runloop() =0; /* called once the thread is started. Should be overloaded by subclasses. */
     void go() ;	// this one calls runloop and also sets the flags correctly when the thread is finished running.