support UTF-8 escaped hexadecimal

[kasperk81]

C/C++, JavaScript, Python and C# support escaped headecimals.

Mañana -> 4D\x61\xC3\xB1\x61\x6E\x61 or modulo ASCII Ma\xC3\xB1ana

please add support for:

• UTF-8 escaped hexadecimal
• UTF-8 escaped hexadecimal except ASCII

[kasperk81]

note: the first one is same as UTF-8 code units except space is replaced by \x