[Open Assets] Retro Bosses + Maces and Chains v2.5

This update mainly focuses on bugfixes and other changes.

Changes:

• The "Resource" and "Example" PK3s have now been merged into one - This should prevent users from trying to load both at the same time and encountering numerous unintended bugs.
• Added text for map Thing flags in Zone Builder - You can now see what each flag does (ex. "End level on death" instead of "Special")!
• Redid the way jet fumes are spawned and positioned - The code is now slightly less redundant!
• Merged the Egg Slimer's "gib" spawning code into one action - The code is now shared between the two versions (2.0 and 2.1); Updating is not necessary, but highly recommended!

Bugfixes/Quality of Life Improvements:

• 2.1 Metal Sonic should no longer disappear in netgames
• Simple Mode:
  • 2.0 Brak missiles can now be turned with the "Move Left" and "Move Right" controls (only in Simple Mode)
  • 2.0/2.1 chains can now be turned left and right without bugging out

This update brings bosses ported from 2.0!

Changes:

• A mostly complete structure overhaul!
  • Many of the objects, sprites, states, actions, etc. that are shared between specific Lua scripts have been separated into their own Lua scripts to make it easier to use in your own mods. As a result, I highly recommend any mods using this addon to use this updated version, in order to decrease redundancy.
• 2.0 maces and chains have been added! Just set the "Extra" flag on a mace or chain map Thing to make it use the 2.0 sprites (does not apply to the hidden chain)!
• MIDI music is now available in the example level pack!
• Skies have been fixed to use their correct counterparts from earlier versions of SRB2.
• The levels in the example level pack now show up in the level select!
• Zone Builder support has been improved.
• Maces now use DMG_SPIKE instead of the generic damage type.

Bugfixes:

• Map Thing spawning has been adjusted for flipped objects to spawn on the ceiling instead of the floor.
• The skybox in 2.1 Brak's arena has been adjusted to be more accurate to its 2.1 counterpart.
• Green Flower is now "properly" spelled as Greenflower in the example level pack.
• Many others that I probably forgot...

Please look at the main post to see what has been included.

This quick update fixes an issue where the player originally couldn't rotate a 2.1 chain controlled by a linedef with the "No Climb" flag set.