Unicode/Emoji literals

[R4wizard]

It's currently not possible to use unicode/emoji characters within an expression without the lexer being unhappy. At the moment non-ASCII characters only work within string literals.

I propose we add the ability for these characters to be used as variable names. This would be useful for non-English and joke applications.

Expected:

const OpenExpression = require('openexpression');
console.log(OpenExpression.evaluate('📈 * 3', {
    '📈': 3
})); // => 9

Actual:

Unexpected character at index 0: