Allow Emoji in Legend/Level Data

[hawkerm]

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Related #115

I'm making a word puzzle with letters, so most of the alphabet is being taken up by defining the letters as readable (v being reserved is a problem for that, but that's a different issue.)

I also was doing shenanigans with teleporters and needed 20 of them. I could do a bunch of weird ascii/unicode symbols I suppose, but emoji are pretty accessible on the keyboard these days, so it'd be nice to have those as an option too.

It'd also be fun for folks learning or more visual to have level definitions like this:

======
LEGEND
======

⬛ = Background
🤺 = Player
📦 = Crate
🧱 = Wall
🎯 = Target

======
LEVELS
======

🧱🧱🧱🧱🧱🧱
🧱🤺⬛⬛⬛🧱
🧱🧱⬛📦⬛🧱
🧱🧱⬛⬛🎯🧱
🧱🧱🧱🧱🧱🧱

[david-pfx]

To be clear, 'v' is not really reserved, but it has a special meaning in rules. You can use it as a legend character (a 'glyph'), you will get a warning, just not in rules.

But it seems that while you can use just about any Unicode character in messages, the rules for legend glyphs are less consistent. I'll see what I can do.

See also #98.