Add a builder with twig support

[szeidler]

Initial approach to fix #3.

The twig template can be used with defining

"builder"      : "kss_styleguide/twig/",

in the kss-config.json file.

There is some room for improvements, to avoid duplication between both builders.

[JordyPouw]

@szeidler Sorry for the late reply. I will look at this later on and try to improve it a bit to prevent duplications. Thnx! :)

[schneyra]

Any chance on bringing this to the next release? I'd love to use my twig templates for the styleguide.