arrows stick to Enemies location; disappear after death
arrows become inert if stuck; (cannot cause damage)
dead enemies drop random items; arrows can be picked up
Commodity class added; within its constructor is the integer "type"; this
"type" is assigned to a specific image also within the constructor (i.e
key, coin, arrows)
Merge pull request #36 from jshiraef/master

Arrow/Enemy collision fixed; Items dropped upon enemy death