added support for BMP180

defines to tell which sensor to use
added support for SHT21

defines to tell which sensor to use
changed to 2 second wake-up

saves waking up too often
tidy up

removed redundant wind calculation timer (work is done in wind.ino)
removed leading spaces to tidy up source code layout
increased sensor settle time to 15 mS
record update every 30 seconds instead of 15 seconds