Added explode class
Merge branch 'master' of github.com:dtak1114/rubycamp2013

* 'master' of github.com:dtak1114/rubycamp2013:
  Background is changed in the amount of dameges.
  new graphics of title,enemy,beach, and fighter
Merge branch 'master' of github.com:dtak1114/rubycamp2013

* 'master' of github.com:dtak1114/rubycamp2013:
  速度が半分にして、はみ出るバグの修正
explode effect added
fixed conflict for main.rb & director.rb
Merge branch 'master' of github.com:dtak1114/rubycamp2013

* 'master' of github.com:dtak1114/rubycamp2013:
  graphic of gameover