[FEATURE] Boss fight

[maxogod]

🚀 Feature

Boss fight after reaching a milestone

Motivation

Brings a greater objective to the game and a reason for players to keep trying to reach a win against the boss

Implementation

After a player reaches a given amount of kills or score or kills of the hardest enemy ship (artillery) the boss fight will start, its health bar will replace the invasion progress bar and the player cannot lose by invasion.

The boss will shoot lasers from several cannons and shoot bombs from the central cannon. When its health decreases to a certain point it will shoot omega laser beams that take up most of the screen.
Additionally it will occasionally deploy lower level ships (common, gliders and fasts).

Additional context

Easter egg: after killing it the game will start over (without resetting the speed) and the player ship will become golden.