[x] Obstacle in the playing field, player character cannot move into it.
[x] Clicking on the map makes the player character shoot a bullet in that direction. Bullet explodes after hitting the obstacle. Explosion spawns particles.
[x] Obstacle has limited health. Upon destruction, obstacle explodes into particles, and a new obstacle is spawned in a random location.
[x] Clickable menu buttons to exit and enter a game session.
Prereqs: #3 #4