Support for multiple alphabets

𝔥𝔦 𝔰𝔲𝔟𝔰𝔱𝔞𝔠𝔨

I've added support for multiple alphabets. There are currently:

 - 𝔣𝔯𝔞𝔨𝔱𝔲𝔯 (default)
 - 🅂🅀🅄🄰🅁🄴🄳
 - 🅽🅴🅶🅰🆃🅸🆅🅴 🆂🆀🆄🅰🆁🅴🅳
 - ⓒⓘⓡⓒⓛⓔⓓ
 - 🅝🅔🅖🅐🅣🅘🅥🅔 🅒🅘🅡🅒🅛🅔🅓
 - ｆｕｌｌｗｉｄｔｈ

However, decoding the new alphabets currently fails. I think it's because the regex in `decode()` only works with the fraktur alphabet. Do you think you could help me with this one? Of course, only if you like the changes.

Best regards  
Max