DOC: tweaks to RatingScale API doc, use setAttrib

- use setattrib-style for pos, color, text, etc
Merge branch 'rf-ratingscale' of github.com:jeremygray/psychopy into rf-ratingscale

* 'rf-ratingscale' of github.com:jeremygray/psychopy:
  DOC: tweaks to RatingScale API doc

Conflicts in doc strings:
	psychopy/visual/ratingscale.py