EEPROM: Add an update function (#780)

According to the Arduino docs, update works just like put, but it first checks if the value is different from the current one.
This is how our put already works, so we just alias update to put and we're done.
Function added to be more compatible with the Arduino API.
Also see #778

libraries/EEPROM/EEPROM.h

@@ -62,6 +62,10 @@ public:
         return t;
     }
 
+    template<typename T>
+    const T &update(int const address, const T &t) {
+        return put(address, t);
+    }
     size_t length() {
         return _size;
     }