Allow setting of custom symbols

[Retoon]

I've noticed some unicode symbols (e.x. the SelectBuilder cursor) is not supported by the windows command line cmd.exe. Having the option to set a custom char would be a nice addition to the library in my opinion. I'm still getting used to the concepts of the rust language itself so i don't have a concrete solution for this, but im assuming the chars for the library are defined as constants somewhere. My proposal is allowing them to be set to a custom char in the same way that PasswordBuilder is able to set a custom masking char, to keep everything nice and consistent.