update build-CI (RobTillaart#2)

* add countAbove(), countLevel(), countBelow(). findMin(), findMax()
* add setBucket(), param for clear()
* update build-CI
* update readme.md + badges
* add histogram8 and histogram16 derived class

Arduino ci (RobTillaart#1)

* initial arduino-ci
* add unit tests

0.2.0 release