add trusted pseudo-classes argument

It useful to wide cssselect pseudo-classes support like `:not()`, `:nth-child()`, `:nth-last-child`, `:nth-of-type()`, `:nth-last-of-type()` and etc.  For this case pseudo-classes as `:hover`, `:active` and etc. will processed but not left in style attribute, so you must use for this `keep_style_tags` argument.