Maybe done a slightly better job of handling the mouse cursor.
Added player bullet firing and refactored the boundary collisions to handle both player and bullets.
Created enemy component and system. Added a simple enemy movement pattern that follows the player.
Added enemies to boundary collision system.
Bullets now kill enemies.
Added a simple enemy spawn timer system.
Move assets into a separate asset class.
Gave each velocity component its own max velocity.
Added an animation system.
Added a lifetime component and lifetime system to give entities a finite lifetime.

Also updated the gradle build file to use the latest (v1.3.0) ashley version.