Glyph support
Picotool currently uses the `'ascii'` encoding when reading and writing .p8 files. I believe this would fail when code contains glyphs.

The glyph representation in .p8 files has changed as of 0.1.11e to use a UTF-8 encoding, so it's likely that the correct solution is to switch to that encoding, then carefully make sure these sequences are converted to binary correctly. It might be worth accepting only the narrowest range of supported code points and not all UTF-8 values. IIRC previous behavior with high chars in Lua source was undefined in Pico-8, usually accepted silently or possibly converted invisibly.

Also, glyphs can now be used in identifiers, so this likely requires an update to the lexer.