DooG V0.98 update

Since I already had an online game server, I decided to expand on it and implement an unlockable achievements system that grants badges when completing specific conditions. You can check out the conditions to unlock each badge by clicking on them in the badges menu.
I also reached out to more artists to include additional illustrations in the gallery, for Hololive Gen 5 and HoloEN.
Additionally, I fixed some bugs in the secret level, which I don't know how long have been there since I haven't test run it in a long time. :P

New stuff:

• Implemented an unlockable achievements system.
• Added HoloEN fanart in Level 1 gallery.
• Added Hololive Gen 5 fanart in Level 1 gallery.

Bug Fixes:

• Fixed bugged walls in secret level.
• Fixed a bugged door in secret level.
• Added missing Exit sign in Level 3 exit room.