Fixed a bug which caused objects to be rendered offset from their center
Fixed a bug which caused isBossTime to be set true when no current enemies, even if there were enemies to be spawned
Fixed some bugs and changed some logic in the hits()  method
Implemented laser
Fixed a problem in engine.js which caused some dead objects to be skipped when removing (index change on deletion)
Added a check whether a movement strategy is provided to self-controlled-object.js
Some refactoring on projectile inheritors
Added laser test image