Grimblast: When saving screenshot, create parent dir if it doesn't exist instead of failing

[LeviVanDerMaas]

Previously, grimblast would fail to save the screenshot if the target file location's parent dir did not exist yet (but it would still notify you that it succesfully saved).

Description of changes

Things done

• For new programs

  • Add the program to the README table, with yourself as the maintainer
  • Add a README for the program itself
  • Add Makefile (and Nix derivation optionally, otherwise @fufexan will do it)
  • If the program is a script, add it to the CI checks matrix

• For changes

  • Add changes to the CHANGELOG
  • Reflect your changes in the man pages (if they exist)

[fufexan]

LGTM, thanks