Make dump() not be anyerror!...

[Arnau478]

It's very tedious to work with a library where the main function does not have a defined error set. The problem is that it uses an AnyWriter, which returns anyerror!... for most functions. Here are some options to fix this:

• Stop using AnyWriter
• Collapse every error that comes from a writer call to a single error.WriteError

[Arnau478]

I think the best approach is to not use AnyWriter at all, and pass an anytype. This has the advantage of having a defined arror set, that can be computed at comptime. Thus, errors are not collapsed either.