Add this to your Gemfile:
gem 'middleman-typogruby', :git => "git://github.com/ssbx/middleman-typogruby.git"
And this to your config.rb (these are the default options):
activate :typogruby do |typo|
typo.entities = false
typo.typeamp = true
typo.caps = true
typo.initial_quotes = true
typo.smartypants = true
typo.widont = true
end
See Typogruby doc for documentation.