Fix multiple --sensor tags and provide tests

[onkobu]

• multiple --sensor parameters yielded repeated output in message and/ or performance metrics
• added tests-infrastructure, purely Bash-driven
• outlined a few terms in README (device, sensor, adapter), also subtle issue with repeated sensor names
• hints on writing tests in README
• merged with upstream master
• new version 1.3, also in HISTORY

[onkobu]

It was a feeling of uncomfortable insecurity @shakalandy's questions left behind. I made some tests and indeed multiple --sensor-parameters yielded repeated outputs of the same sensor.

I'm also able to explain my initial issue more clearly: First of all I mixed up sensor and device. That's why I added the small section about sensors to the README. In turn my hardware has multiple devices that all use the same sensor-name temp1. That's why I had issues with the simple combination of sensors | awk.

The -n switch introduced with my first PR mitigates this by invoking sensors <sensor> | awk instead. But now --sensor is the device the sensor belongs to – I officially ask for a better idea based on this second PR.

Finally I added some test infrastructure I (and hopefully others) don't break it again with "just a minor change". It is also a good method of collecting sample invocations without possessing the hardware.