fixed Vector#/ spec division by zero
Surface#fill_rectangle -> #fill; Surface#fill fills entire surface without position args
Game#screen
Surface#draw
extended Entity#draw
fixed Vector#/ spec division by 0
Desktop#render
Game#playing[=]
replaced Game#playing with Game#start/#stop/#started[=]
Desktop#each_tick
Desktop#tickrate
removed Game#started[=]/stop, extended Game#start
made Entity::new more Yeahful
extended Game#draw
fixed rounding error in Desktop#tickrate[=] specs
Game#draw preclears screen