fix compiling issues on AVR platforms without standard <functional> libraries

Author: alvarolb

src/ThingerClient.h

@@ -28,6 +28,11 @@
 #include <Client.h>
 #include "thinger/thinger.h"
 
+// required for the reboot method (wdt_enable)
+#if defined(ARDUINO_ARCH_MEGAAVR) || defined(__AVR__)
+#include <avr/wdt.h>
+#endif
+
 using namespace protoson;
 
 #ifndef THINGER_SERVER
@@ -430,7 +435,12 @@ class ThingerClient : public thinger::thinger {
                 break;
         }
         #endif
+
+#ifdef THINGER_USE_FUNCTIONAL
         if(state_listener_) state_listener_(state);
+#else
+        if(state_listener_!=nullptr) state_listener_(state);
+#endif
     }
 
     bool handle_connection()
@@ -542,9 +552,15 @@ class ThingerClient : public thinger::thinger {
         return root_ca_;
     }
 
+#ifdef THINGER_USE_FUNCTIONAL
     void set_state_listener(std::function<void(THINGER_STATE)> state_listener){
         state_listener_ = state_listener;
     }
+#else
+    void set_state_listener(void (*state_listener)(THINGER_STATE)){
+        state_listener_ = state_listener;
+    }
+#endif
 
     Client& get_client(){
         return client_;
@@ -558,7 +574,12 @@ class ThingerClient : public thinger::thinger {
     const char* device_password_;
     const char* host_;
     const char* root_ca_;
+#ifdef THINGER_USE_FUNCTIONAL
     std::function<void(THINGER_STATE)> state_listener_;
+#else
+    void (*state_listener_)(THINGER_STATE) = nullptr;
+#endif
+
 #ifndef THINGER_DISABLE_OUTPUT_BUFFER
     uint8_t * out_buffer_;
     size_t out_size_;

src/thinger/thinger_resource.hpp

@@ -103,7 +103,9 @@ class thinger_resource {
     unsigned long last_streaming_;
 
     // used for thenables (code after running a resource)
+#ifdef THINGER_USE_FUNCTIONAL
     std::function<void()> then_;
+#endif
 
 #ifdef THINGER_ENABLE_STREAM_LISTENER
 #ifdef THINGER_USE_FUNCTIONAL
@@ -302,6 +304,19 @@ class thinger_resource {
         callback_.pson_in_pson_out = pson_in_pson_out_function;
     }
 
+    /**
+     * Establish a function that will be called after executing the resource
+     */
+    void then(std::function<void()> then){
+        then_ = then;
+    }
+
+    /**
+     * Run the configured 'then' resource function, if any
+     */
+    void then(){
+        if(then_) then_();
+    }
 
 #ifdef THINGER_ENABLE_STREAM_LISTENER
     /**
@@ -319,20 +334,6 @@ class thinger_resource {
     }
 #endif
 
-    /**
-     * Establish a function that will be called after executing the resource
-     */
-    void then(std::function<void()> then){
-        then_ = then;
-    }
-
-    /**
-     * Run the configured 'then' resource function, if any
-     */
-    void then(){
-        if(then_) then_();
-    }
-
 #else
 
     /**