Tricenz-64 now with #include

With this new version, we introduce an #include statement. This makes it easier to reuse code and to kick things off we have a little library to show a menu. As a technical note, the files are only included once (even if referenced from multiple other files).

One thing I added last update but forgot to highlight: we now have "cheatsheet.txt", all of Tricenz-64 in a single page.