Remove serial.print from library and update example error handling. Resolves issue #11 and #13.

DHT.cpp

@@ -46,7 +46,6 @@ float DHT::readTemperature(bool S) {
       return f;
     }
   }
-  Serial.print("Read fail");
   return NAN;
 }
 
@@ -70,7 +69,6 @@ float DHT::readHumidity(void) {
       return f;
     }
   }
-  Serial.print("Read fail");
   return NAN;
 }