Enable smoothscroll for soft wrap mode

[reedes]

I read that vim has a new "set smoothscroll" feature that reduces the jumpiness of long lines of soft-wrapped text.

Available in version 9.0.0640, per a post on reddit. This would need to be verified and enabled conditionally like pencil handles other version-dependent features.

Ideally, like other pencil features it would be enabled when pencil initializes for the current buffer and be restored to original setting when pencil is turned off for that buffer.