Library routines to support clipboard formats

[dansanderson]

PICO-8 has yet more data formats to serialize cart data of various types on the clipboard, suitable for inlining in a BBS post. It'd be cool if this could be yet another format picotool can read and write.

I'm not sure what the tool interface would be. It would probably just be library routines for use in other tools, such as a web app that allows you to paste clipboard pieces into an existing cart. A command-line tool could use pipes with macOS's pbcopy/pbpaste or Linux's xclip.