Feature: Character buffer block

[Unexian]

Describe your feature or enhancement suggestion
Add a cipher block that allows you to add character buffers to the start or end of each word.

Describe a concrete use case
Decoding through numeral system then polybius square. The program errors if one of the outputs of the polybius square block starts with a 0 as it isn't represented when decoding using the numeral system block.