http://raspi.tv/2013/how-to-use-wiringpi2-for-python-on-the-raspberry-pi-in-raspbian
http://wiringpi.com/wp-content/uploads/2013/03/pins.pdf
http://www.element14.com/community/docs/DOC-73950/l/raspberry-pi-2-model-b-gpio-40-pin-block-pinout
https://www.sparkfun.com/datasheets/Sensors/Temperature/DHT22.pdf
http://www.cnblogs.com/sn-dnv-aps/p/4390899.html
