Added HTU21 Sensor (#588)

* Added HTU21 Sensor Support

Co-authored-by: Jonathan Wells <jonathan-wells@oist.jp>

main/config_HTU21.h

@@ -0,0 +1,56 @@
+/*  
+  OpenMQTTGateway Addon  - ESP8266 or Arduino program for home automation 
+ 
+   Act as a wifi or ethernet gateway between your 433mhz/infrared IR signal  and a MQTT broker
+   Send and receiving command by MQTT
+   
+   This is the Climate Addon:
+   - Measures Temperature, Humidity and Pressure
+   - Generates Values for: Temperature in degrees C and F, Humidity in %, Pressure in Pa, Altitude in Meter and Feet
+   - Required Hardware Module: HTU21
+   - Required Library: SparkFun HTU21 Library v1.1.3
+
+   Connection Schemata:
+   --------------------
+
+   HTU21 ------> Arduino Uno ----------> ESP8266
+   ==============================================
+   Vcc ---------> 5V -------------------> Vu (5V)
+   GND ---------> GND ------------------> GND
+   SCL ---------> Pin A5 ---------------> D1
+   SDA ---------> Pin A4 ---------------> D2
+   
+    This file is part of OpenMQTTGateway.
+    
+    OpenMQTTGateway is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenMQTTGateway is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef config_HTU21_h
+#define config_HTU21_h
+
+extern void setupHTU21();
+extern void HTU21toMQTT();
+
+#define htu21_always true // if false when the current value of the parameter is the same as previous one don't send it by MQTT
+#define TimeBetweenReadinghtu21 30000
+
+/*----------------------------USER PARAMETERS-----------------------------*/
+/*-------------DEFINE YOUR MQTT PARAMETERS BELOW----------------*/
+#define HTUTOPIC   "/CLIMAtoMQTT/htu"
+
+#if defined(ESP32)
+  #define I2C_SDA 16
+  #define I2C_SCL 0
+#endif
+
+#endif