Stress-injector

- Stop the thread that measures CPU usage during a manual interrupt
- Previously CPUStress measurement used to run until the current time reaches 3 seconds in addition to the user input.
- Since the measurement runs in a dedicated thread this, stopping stress never stopped the usage display.
- Now CPUStress measurement will stop when a manual interrupt is received using a stop_flag variable.
- Update docs and README.md internal link.

- Fix broken CPU stress because of global variable
- Wrap everything inside a class
- Add an option to pass the user input when the class is initialized
- Update dependencies, docs and readme
- Update variable names to right convention

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- Mark methods as internal
- Update dependencies and readme