BBC, CPC, C64, ST: quality of life

Some quality-of-life improvements in this release (i.e. absolutely no changes to the story file):

• The interpreter for the BBC and Acorn computers has been upgraded: it now boasts faster loading times and fits on a single-sided disk!
• The loader screen for the C64 and the Amstrad CPC have been improved.
• The Atari ST programs and files inside the .st file are now included in a separate folder, for greater ease of use on real hardware. Copy everything in "contents" onto a floppy to get the same thing as the ".st" file.

I will now work on fixing a few bugs in the story file; expect Release 2 of the story file this weekend. Thank you!