v0.1 demo

[OrangeJuice7]

• [x] Controllable player character. WASD to move.
• [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

[OrangeJuice7]

Left to do:

• Obstacles are immovable (define a Building entity?) Left to #27
• [x] Obstacle respawns