Add unit tests and continuous integration

[s-celles]

Hello,

I'm considering this library as a dependency for an application.
Althought I'd prefer to rely on a library which have unit tests.

You can find some links dealing with continuous integration and Arduino
https://github.com/adafruit/travis-ci-arduino
https://www.pololu.com/blog/654/continuous-testing-for-arduino-libraries-using-platformio-and-travis-ci
(they are using http://platformio.org/ )

Kind regards

PS : see also https://docs.travis-ci.com/user/integration/platformio/

https://github.com/platformio/platformio-remote-unit-testing-example

See also https://github.com/mmurdoch/arduinounit/

See discussion mmurdoch/arduinounit#63

[ivanseidel]

This got merged!