Author and license should be added to the BASIC programs

[mobluse]

According to CONTRIBUTING.md BASIC programs should have author and license in the head of the file using REMs:
"Do not forget to add AUTHOR AND LICENSE information in the head of the file via REMs"
Only one of the programs have this AFAIK: aritm-x16.bas. I think author and license should be added to the BASIC programs that doesn't have this already using REMs in the first few lines of the program.

[edthedev]

What is the preferred license?

[edthedev]

It could be worth updating the contributions guide to recommend a license.

I've gone with GPLV3 to be consistent with aritm-x16.bas, but will be happy to re-license if needed.