More minor updates

[terrillmoore]

I thought I pushed these earlier, but evidently I did not.

The individual commits are pretty clearly separated.

• 3d85501 makes otaasensor.ino and otaa-sigmap.ino work with the latest library.
• d482613 fixes the documentation (only) in 3d85501.
• 9070b05 and cf3ede2 change otaasensor.ino so that it starts and runs whether USB is connected or not.

It is possible that otaa-sigmap.ino is out of date relative to work that Frank Rose has done with mapthethings.