Added DHT library to extras and sample code to examples

extras/dht/dht.h

@@ -0,0 +1,17 @@
+/*
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 Jonathan Hartsuiker (https://github.com/jsuiker)
+ * BSD Licensed as described in the file LICENSE
+ *
+ */
+
+#ifndef __DTH_H__
+#define __DHT_H__
+
+#include "FreeRTOS.h"
+
+bool dht_wait_for_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_sate, uint8_t * counter);
+bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature);
+
+#endif
+