Fix getPiRevision to check for revision value 0002 or 0003 as rev 1 boards.
Fix bug with readS16 not returning signed results, and add optional explicit endian parameter to 16 bit reads.
Remove debug log from readS16 to prevent double logging.
Fix bug in calling readU16 from readS16.
Merge pull request #82 from adafruit/i2c_fixes

Fix bugs with getPiRevision and readS16