lower the minimal sampling interval

[soundanalogous]

The current minimal sampling interval of 10ms was set back when Arduino boards still used the ATMega168. The newer SAM architecture boards can likely handle a lower sampling interval. Determine a new minimal value.

[soundanalogous]

Also, for Firmata 3.0, consider the ability to set a sampling interval per feature.

[rwaldron]

Nice!

[soundanalogous]

done