Merge pull request #46 from BU-CS673/graphics

Graphics
Merge pull request #52 from BU-CS673/graphics

Graphics
add explosion & tank image

1. add 3 explosion image
2. add 2 tank image
Question about initialization

I put my question in the comment. It seems to me that they need to be
initialized.
Revert "Question about initialization"

This reverts commit ca0097abd053a0409b66ed0e92f0713288a06212.
Combine 3 explision png files into 1 gif file
tank&explosion png

delete explosion.gif
delete tank_blue.png/tank_green.png
add tank.png
add explosion.png
Merge pull request #53 from BU-CS673/Chennan

Chennan -> Graphics
first commit
Merge branch 'graphics' of https://github.com/BU-CS673/bubolo into Aditi