Convert to busdevice use.

[caternuson]

This library is using the I2C bus directly and manually managing locking/unlocking. It should be converted to use BusDevice. See example here.

[ladyada]

yah this was one of the first libraries written :)

[caternuson]

Yep, was just doing some housekeeping and came across your comment in #7. Figured a separate issue would be good for tracking and visibility.

[caternuson]

Fixed with #9