Add tests for RUNE-DOWNCASE.
Add tests for RUNE-DOWNCASE.

attila-lendvai/iolib,sionescu/iolib,attila-lendvai/iolib,shamazmazum/iolib,dkochmanski/iolib,sionescu/iolib,tiago4orion/iolib,tiago4orion/iolib,attila-lendvai/iolib,deadtrickster/iolib,dkochmanski/iolib,shamazmazum/iolib,deadtrickster/iolib,vsedach/iolib-simple-mux,deadtrickster/iolib,sionescu/iolib,tiago4orion/iolib,lispnik/iolib,dkochmanski/iolib,lispnik/iolib,lispnik/iolib,vsedach/iolib-simple-mux,shamazmazum/iolib