Continuous integration

[acherm]

We're missing testing procedures to check that everything goes fine when pushed... Some TODOs

• [ ] define the "tests": tinyconfig and defconfig seems OK, we can perhaps play a bit with the parameters (compiler version) and randconfig
• [ ] might be nice to have as output a structured information (in JSON?) when kernels are build for observing that indeed everything works fine
• [ ] gitlabci / Github Travis/actions