User programmable resolution

Hi Gordon, are you interested in adding support for this chip features? I've implemented user programmable resolution, mostly because I believe 9-bit readings are much more meaningful (and faster!) than default 12-bit.

Bad news is that it makes this library use up more memory, good news is that half of new code (read/write scratchpad) can be reused for another missing features I want to look at - alarms and CRC.