Academic exercise done for Computer Graphics class at UFES, 2012/2.
Updated the Makefile to enable partial builds.
Added a handicap to enemy tanks

Created a multiplier applied to enemy tanks reload timer, so the player
fires faster and has a better chance at winning.
Code clean up.
Fixed a bug where some agents weren't being updated

After some agent was being destroyed, the next one in the agents array was
being skipped.
A game over state detection and message was added to terminate the game cleanly.