Adds ctypes wrapper for DHT sensors

[nebulans]

Modifies DHT C code to give a read function that returns temp and humidity, and a ctypes python class wrapper for this. Updates the python example code to use this instead of subprocess.

Behaviour of C code unchanged when called from terminal.

Needs testing on DHT11 type sensors, I only have a DHT22.

[etienned]

Very interesting! Unfortunately when I test it I got OSError: ./libAdafruit_DHT.so: undefined symbol: bcm2835_gpio_lev.

I compiled the lib like this (you should modify the Makefile to produce the lib in your patch, no?):

$ gcc -std=c99 -l bcm2835 -shared -o libAdafruit_DHT.so -fPIC Adafruit_DHT.c

I have already compiled and installed lcbm2835. Any clues?

Thanks

[nebulans]

Not really, I'm no C expert. I just hacked it to get it to work nicely with the python in my case. I'm away from the Pi I've got this running on with the hardware for a little while but I'll get back to you once I've had a chance to fiddle with it again.

[tdicola]

Thanks for sending the pull request and apologies that it couldn't be reviewed earlier. We've actually deprecated this Adafruit_DHT_Driver code and refactored the DHT sensor reading C code into the Adafruit_Python_DHT library here: https://github.com/adafruit/Adafruit_Python_DHT I'll close this pull since the new library is the source for DHT interface code going forward. Thanks again for sending the pull request!