allow passing functions directly

[ahorek]

my intention is to fix thread safety problems #133 and rails/sprockets#581
and eventually remove
https://github.com/rails/sprockets/blob/0cb3314368f9f9e84343ebedcc09c7137e920bc4/lib/sprockets/utils.rb#L126

sassc doesn't allow you to use different functions for different contexts easily

you can customize functions by patching Sassc::Script::Functions, but there's a race condition if you do this at runtime

this patch will allow you to pass custom functions like this

module MyModule
  def asset_path(path, _options = {})
  end
end

SassC::Engine.new(sass, style: :compressed).render # default Sassc::Script::Functions
SassC::Engine.new(sass, style: :compressed, functions: MyModule).render # custom

what do you think?

[diabolo]

Any chance for this to be released?