v0.2.3: multiple: Implement `fmt.Stringer` for a Bunch of Types (#117)

* wdte: Implement `fmt.Stringer` for `GoFunc`, `Scope`, and `ScopedFunc`.

Also, switch to `strings.Builder`. Go 1.11 is out now, so I don't think
I have to worry too much about compatability problems. Hopefully.

* wdte: Implement `fmt.Stringer` for `Array` and tweak `Scope.String()`.

* std/io: Implement `fmt.Stringer` for `Reader` and `Writer`.

Also, clarify the documentation for those types a bit.

* std/io: Implement special `fmt.Stringer` handling for std{in,out,err}.

* std/io: Actually use stdout for stdout.

Holy crud. How long has that bug been there?

* std/io: Defer the `fmt.Stringer` implementation upwards for std{in,out,err}.

This removes the specialness of the handling.

* std/io: Fix a typo.

* std/io/file: Implement `fmt.Stringer` for `File`.

* std/stream: Implement a very basic `fmt.Stringer` for every type.

* std/arrays: Implement `fmt.Stringer` for the `Stream` implementation.