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'll check this, but you'd need to tell the player if they're getting knocked down.  Probably worth involving Dodge here too (and granting Dodge practice for the roll) so characters can improve their blade-fighting skills.

(Hockey players IRL seem to maneuver pretty well.)