Automated tests

[EnotionZ]

Use some free CI service so we can catch something like https://github.com/EnotionZ/GpiO/issues/47

[rzr]

I can add a dockerfile and travis job if it helps

[makeros]

You can try to mock the environment for gpio on the hardware. Right now i'm using something like this https://github.com/Ozsie/gpioMock/ (modified a little bit) to mock the behaviour of a gpio files tree. Testing for temperature sensors. I can now control the sensor values by providing a function which is calculating the changes during time.

[EnotionZ]

@makeros thanks for sharing, I'll consider using gpioMock for this. Looks like that library can also resolve #40. Also related to #51.