Fix goofy call to start()

This was highlighted by tableflip/nodebot-workshop#9 and
nodeschool/discussions#298 and fixes those issues. Added new method
resume() which resumes the motor’s last set speed instead of depending
on start().
v0.8.1

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Remove unused ESC parameters

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

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
v0.8.2

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

In the playTune test there was just 4ms of wiggle room for the tune to
finish. In Travis this failed about half the time (only 3 calls were
made on freqSpy). I added 20ms of wiggle room to the timeout.

Also in toneStopsAfterTime the test was inermittently firing before the
tone had finished playing. I added 10 ms of wiggle room there.
Merge pull request #416 from dtex/piezo-test-fixes

Piezo test fix