Constant radix64::FAST

pub const FAST: Fast

Encode and Decode using a fast alphabet with no padding.

This is not part of any official specification and should only be used when interoperability is not a concern. The alphabet used is
:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz
It's specifically tailored for fast encoding and decoding when AVX2 is in use.