Enable A7 for PWM, cause it works. It is needed for using the shield shield with a L298 shield with the default configuration.
Update to address proper indexing of servo array
Pins A4 and A5 also support PWM just fine
Correct comment to proper number
A6 supports PWM too, as well as correcting the pin reference
Cleanup on disconnect

The program on the spark runs forever which means that any state created by one connection would be persisted to the next connection.

- reset values in pin reading list
- reset values in pin previous list
- detach servos

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Correct pin indexes for A4-A7 (14-17)

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>