Misc. updates for this new iteration:
- pass to python 3 and clean the code
- rely in python template engine for SystemVerilog and cpp generated files
- add more information in README
- move to GitHub Actions and enhance the regression scope
- start a first support of Verilator. Execution is OK, needs to enhance cpp template and prepare a svut.h to bring equivalent SystemVerilog macros in C++ world. Will be probably minimal and based on existing unit test flow