unique index creation breaks on mysql innodb + utf8mb4 + charfield
Dude...

Just subclass charfield and provide a default maxlength and use that.

hi,

I found that the default CharField() is a varchar of length 255, this makes mysql throw error 1071 because in innodb the maximum length of a index is 767 bytes (~190 utf8mb4).  default utf8 will fit 255 chars.

Would it be possible to have peewee detect that the database is using utf8mb4 and adjust it accordingly? or should I be creating a UTF8MB4CharField() and make it do CharFIeld(max_length=190) ?
