CI improvements

Now Github Actions are in use for some checks and continuous integration.

minor improvements

removed compiler warnings
racing condition in noDataSince function.

optimization and removed compiler warnings.

Pull request:

• #17 Remove unnecessary comarisons

Issues:

• #18 Build is "noisy" when Arduino Compiler Warnings = All selected.
• #19 Build warning when Compler Warnings = All (Part 2)
• #20 Build warning when Compler Warnings = All (Part 3)

Stable

Sensor support added.

Arduino 1.6.x compatibility

fixed datatype Errors.

Release for Arduino 1.6.x library manager

some corrections to make the library usable in the Arduino Library Manager