hex / bases decode

[elig0n]

Would love to see [h & ]h (or similar) for hex encode & decode and even other bases.

[tpope]

The limitation here is we're running low on maps. ]h isn't great because the linewise map would be ]hh, which is ambiguous with "decode one character to the left".

[doubledup]

It's pretty clunky, but I ended up using numbers, like ]2, ]6 and ]8 for base 2, 16 and 8 conversions. Also set up ]4 for base64. Are these maps acceptable?

If so I'm happy to open a PR for them. Used some external commands for the conversions, so I'm not sure about portability but I think I stuck to generally available commands.