Ansi should implement java.lang.Appendable

[buko]

Methods like DateTimeFormatter#formatTo take a java.lang.Appendable. Normally this is just a StringBuilder. The Ansi class has an underlying StringBuilder but provides no accessor for its underlying StringBuilder -- which is fine, in this case StringBuilder is just an implementation detail -- but this makes the Ansi class unergonomic when using code that expects an Appendable. I think Ansi should implement Appendable and therefore it should be possible to pass to methods like formatTo that expect an Appendable.