Unlock/Achievement system

[rilifon]

To improve the feeling of game progression and reward the player for each milestone they do on the game, I thought about experimenting with in-game achievements/challenges.

First, remove life-gain with points. Instead, players have a set number of lifes in the beginning, and can permanently increase this number by completing certain challenges. This also syncs a bit with the "lore", since to finish the game we wouldn't want to explicitly influence the player to kill more stuff.

Make initially the player have only one ultrablast, and increase this number with harder challenges.

Suggestion of challenges:

Give extra lifes for:

• Finishing a level part for the first time
• Finishing a level part/complete level with X points
• Finish a level part/complete level killing at most X enemies
• Finish a level part/complete level killing at least X enemies
• Finish a level part/complete level dying at most X times

Give extra ultrablasts for:

• Finishing a level for the first time