Enum entries with non-ascii characters get removed

[Emill]

enum Siffra {
    ETT,
    TVÅ,
    TRE
};

This code works fine in gcc and clang, but when using magic_enum with it, it only detects ETT and TRE.

It seems the pretty_name function in magic_enum only allows 0-9, a-z, A-Z and _. Annex E in the C++ standard seems to allow these kind of characters in identifiers.

FYI, __PRETTY_FUNCTION__ includes this for TVÅ: [E = Siffra, V = TV\303\205].

[Neargye]

Fixed #95