OK, I'll make the `Char = immutable char` change.

> This is something I've thought of introducing in byLine too anyways, to be able to myFile.byLine!dchar().

I understand now. That would work, although I have wondered about solving this by adding an overload that requires `terminator` to be passed explicitly as the first argument:

    byLine(Char, Terminator)(Terminator terminator, KeepTerminator kt = KeepTerminator.no)

This would be more flexible as `"\r\n"` is usually needed on Windows, and this would be clearer to people who may assume `file.byLine()` is portable with line endings.

This overload could replace the other two, which could potentially be deprecated.