#216 Fix type annotation for get_default_settings

[Dmitry Shachnev]

It accepts classes themselves, not instances of those classes.

This fixes error from mypy that I have for code that calls get_default_settings(Writer).

error: Argument 1 to "get_default_settings" has incompatible type "type[Writer]"; expected "SettingsSpec"  [arg-type]

[Günter Milde]

Applied in [r10294].
Thank you for the patch.