Merge pull request adafruit#27 from brentru/fix-autodoc

Fix autodoc

Changes to the tone function (adafruit#24)

* Changes to the tone function:
- uses a fixed length square wave as default (can be variable) like in the mega demo
- frequency is now a float instead of an int

linted and added example

add pylint to project and updated code

fix for gemma/trinket and other non-audio boards

Introduced tone helper modeled after arduino's tone. Works on digital…

… and analog pins. (adafruit#12)

Fixes adafruit#2

shift_in/shift_out (adafruit#11)

Add `shift_in` and `shift_out` modeled after Arduino's `shiftIn` and `shiftOut`.

Correct filename

Add travis config.

Switch from nativeio to digitalio because nativeio was split.

Switch from nativeio to digitalio because nativeio was split.