Make boolean rule properties generate query-style methods

[Sija]

class Foo < Ameba::Rule::Base
  properties do
    description "Disallows foos and possibly bars"
    exclude_bar false
  end
end

# This class definition adds 
# - Foo#exclude_bar (before)
# - Foo#exclude_bar? (now)

[veelenga]

LGTM