cc64 v0.13.1

v0.13.1 contains no code changes. The only change is around the .d64 distribution files in the release:

For the Commander X16, there's a new d64 image cc64-x16files.d64 for
Commander X16 setups with 1541 drive(s).
And to the cc64-c64files.d64 and cc64-c16files.d64 images, a few newer sample files were added that had not been included in these images before.