Remove unmaintainable sanitizer rules. No need to add special "class"
regexp rules anymore, use RenderInternal.SafeAttr instead, more details
(and examples) are in the tests
When reviewing PRs, some color names might be mentioned, the
`transformCodeSpan` (which calls `css.ColorHandler`) considered it as a
valid color, but actually it shouldn't be rendered as a color codespan.
wxiaoguang