Adds a github action which runs the pph script and checks if this introduces changes.

Problem:
- `sml.hpp` generation using `tools/pph.sh` is out of date with `sml.hpp`.

Solution:
- Update files in sml/ folder to fix the generated `sml.hpp`.

Problem:
- There is no example showig how to print state names using a visitor.
- There is no easy support to print sub State Machines state names.

Solution:
- Add example to print state names using a custom visitor and a composite State Machine.

…ers`

Problem:
- ""_s is using a GNU extension to produce an aux::string.

Solution:
- C++20 `non-type template parameters` instead if available.

Note:
- That makes SML C++20 standard compliant.

Problem:
- GCC >=10 doesn't compile with `array[0]` trick to make SML as small as possible.

Solution:
- Remove the zero sized array trick for GCC >= 10.
- Disable sizeof verifcation for GCC >= 10.

Note:
- Another solution has to be considered/implemented.

Problem:
- Support of GCC >= 10 has been fixed.

Solution:
- Update the minor version to `1.1.2`