tsl2550: driver for the TSL2550 light sensor

Change-Id: I9e1c87132404509ffec8bf22a8c6cc993df1aa73
sht21: driver for the SHT21 humidity & temp sensor

Change-Id: Ia71168e394a7b260019e74973db6c9d75d3d4482
bmp085: work-in-progress

Change-Id: I5c297a7f4f8cea2549e537df30a5c7bf5b9d8b51