This makes it easier to extend and modify Haml. The change was originally motivated by issue #570.
Change braces to backticks so generating docs doesn't try to create link to `Sass::Plugin`. Use backticks to format as code instead. This removes warning "Cannot resolve link to Sass::Plugin" that was being generated.
When attribute values contain both an apostrophe and a double quote, we should substitute the character being used to wrap the value with its key code instead of named/keyword entities (for IE support). Fixes #418. Signed-off-by: Norman Clarke <firstname.lastname@example.org>