Sensors: TSL2591

TSL2591 library conversion

Procedure

1. Stared with Adafruit's Adafruit_TSL2591_Library

   https://github.com/adafruit/Adafruit_TSL2591_Library

2. Replaced the Adrino's reads and writes with call to the wiringPi library
3. Sanity checked the code against this JS program:

   https://github.com/bbx10/tsl2591-node/blob/master/tsl2591.js

4. Tested it and fixed a "bug".