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.
added spawning and some fixes

added spawning groups and fixed price and dodge skill dependency
more fixes
Fix comma, melee.cpp syntax issues

Moved the dodge divisor inside and fixed the parens.  Added a comma to
the JSON.