The CommandExecutor helper class can execute shell commands in blocking and non-blocking mode
This class is able to execute processes by using the Linux popen call. It also has the capability of writing
the read output of a process into a provided ring buffer.
The executor works by first loading the command which should be executed and specifying whether
it should be executed blocking or non-blocking. After that, execution can be started with the execute call.
Using non-blocking mode allows to execute commands which might take a longer time in the background,
and allowing the user thread to check completion status with the check function
Moved to HAL like requested in code review and unit tested with failing commands as well.
Also, Linux HAL components are compiled by default now unless explicitely disabled.
This PR introduces the generation of documentation based on
this excellent blog post: https://devblogs.microsoft.com/cppblog/clear-functional-c-documentation-with-sphinx-breathe-doxygen-cmake/
It combines the tools Sphinx, Doxygen and Breathe to generate good
looking HTML documentation conveniently which can be hosted easily.
The helper scripts were unified and there is now one helper.py script
which can be used to create, build and open both tests and documentation.
"./helper.py -h" can be used to get the different options.
This PR also contains some smaller fixes which were necessary for the docs
to build
