Create Linux wheels

Wheels (.whl) are precompiled python packages which do not need any additional compiler. They are platform and python version specific. Currently, we only ship a universal tar.gz file which has to be compiled every time using a c compiler. With some tiny tweaks we can at least ship Linux wheels which makes compiling in these systems superfluous.

I will look if I can extend the CI also for Mac and Linux, but the gitlab ci does not make this easy...