rollerblade skates item proposal

Initial commit for the proposal of rollerblades item, a type of shoe
that offers double movement speed on flat ground, but half otherwise and
has a chance to get you knocked down if used while getting attacked.
Open to suggestions.
I based the price on other similar items. I'm not actually sure how it converts to in-game money, and also, I'm not sure how prices in-game relate to irl prices, but if you say it should be 10 times less, I trust you. =3