add errorToString function

libraries/ESP8266HTTPClient/examples/BasicHttpClient/BasicHttpClient.ino

@@ -61,7 +61,7 @@ void loop() {
                 USE_SERIAL.println(payload);
             }
         } else {
-            USE_SERIAL.print("[HTTP] GET... failed, no connection or no HTTP server\n");
+            USE_SERIAL.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());
         }
 
         http.end();

libraries/ESP8266HTTPClient/examples/ReuseConnection/ReuseConnection.ino

@@ -56,7 +56,7 @@ void loop() {
                 http.writeToStream(&USE_SERIAL);
             }
         } else {
-            USE_SERIAL.print("[HTTP] GET... failed, no connection or no HTTP server\n");
+            USE_SERIAL.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());
         }
 
         http.end();

libraries/ESP8266HTTPClient/examples/StreamHttpClient/StreamHttpClient.ino

@@ -90,7 +90,7 @@ void loop() {
 
             }
         } else {
-            USE_SERIAL.print("[HTTP] GET... failed, no connection or no HTTP server\n");
+            USE_SERIAL.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());
         }
 
         http.end();

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -454,6 +454,33 @@ String HTTPClient::getString(void) {
     return sstring;
 }
 
+/**
+ * converts error code to String
+ * @param error int
+ * @return String
+ */
+String HTTPClient::errorToString(int error) {
+    switch(error) {
+        case HTTPC_ERROR_CONNECTION_REFUSED:
+            return String("connection refused");
+        case HTTPC_ERROR_SEND_HEADER_FAILED:
+            return String("send header failed");
+        case HTTPC_ERROR_SEND_PAYLOAD_FAILED:
+            return String("send payload failed");
+        case HTTPC_ERROR_NOT_CONNECTED:
+            return String("not connected");
+        case HTTPC_ERROR_CONNECTION_LOST:
+            return String("connection lost");
+        case HTTPC_ERROR_NO_STREAM:
+            return String("no stream");
+        case HTTPC_ERROR_NO_HTTP_SERVER:
+            return String("no HTTP server");
+        default:
+            return String();
+    }
+}
+
+
 /**
  * adds Header to the request
  * @param name

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.h

@@ -147,6 +147,8 @@ class HTTPClient {
         int writeToStream(Stream * stream);
         String getString(void);
 
+        String errorToString(int error);
+
     protected:
 
         struct RequestArgument {