cleanup: Changes for c++17

This cleanup adjusts the rTorrent code to comply with c++17 standard. It also simplifies various parts of the code.

src/input/manager.cc

@@ -64,7 +64,7 @@ Manager::pressed(int key) {
   if (m_textInput != NULL)
     m_textInput->pressed(key);
   else
-    std::find_if(rbegin(), rend(), std::bind2nd(std::mem_fun(&Bindings::pressed), key));
+    std::find_if(rbegin(), rend(), [&key](Bindings* bind) { return bind->pressed(key); });
 }
 
 }