Add message/comment on generated files

[mingodad]

Would be nice to have at the top of generated files a comment/message telling it and pointing out the procedure/script that does it, maybe something like in here :
https://github.com/BlueMagnificent/wxUrho3D/blob/e1ecd7ed44bfd3c8f5ec009e10b2c29573a2d56b/gui.h#L1C1-L6C76

[robertoraggi]

Yes, it is a good idea. I usually do it, but in this project it is a bit tricky because it partially regenerates itself from the changes in C++ code, some of the files are fully generated others are partially generated. I will generalize a bit the generators and try to make more explicit on which part of the code is modified.

[mingodad]

Thank you for reply !
Yes I've noticed that you are parsing src/parser/ast.h and then generating other files and ast.h itself again, in those cases adding these remarks would help people trying to contribute/use this project.

[robertoraggi]

@mingodad thanks for your PR. I merged it.