Add skeleton for HTU21DF driver

src/mgos_htu21df_internal.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "mgos.h"
+#include "mgos_i2c.h"
+#include "mgos_htu21df.h"
+#include <math.h>
+
+#define MGOS_HTU21DF_DEFAULT_I2CADDR       (0x40)
+
+#define MGOS_HTU21DF_READTEMP              (0xE3)
+#define MGOS_HTU21DF_READHUM               (0xE5)
+#define MGOS_HTU21DF_WRITEREG              (0xE6)
+#define MGOS_HTU21DF_READREG               (0xE7)
+#define MGOS_HTU21DF_RESET                 (0xFE)
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct mgos_htu21df {
+  struct mgos_i2c *i2c;
+  uint8_t i2caddr;
+  double last_read_time;
+
+  float humidity, temperature;
+};
+
+#ifdef __cplusplus
+}
+#endif