Add test cases to cover the formatting bugs
Fix emoji, user/floor metion in code/pre
Fix underscores in user metion
Add rake task markdown_body:refresh to fix existing invalid HTML body
replace username with place holder to avoid markdown emphasis
fix private method `image_alt` in markdown.rb
Test @small_fish__ in highlighted ruby code block
Fix failed spec caused by Nokogiri escape
New pygments.rb version.