Add MF_RING Mobj Flag (Resolves #164)

This merge request creates the MF_RING flag, which unifies the logic of all ring objects, coins, spheres, ring panels, and NiGHTS stars/chips. Also in this merge request is everything from !2002, but with MF_RING used instead of MF2_FIRING. Please note I have not tested absolutely every change this merge request makes, seeing as there are alot, so please feel free to test it if you'd like.

Test exe: ringflag.exe

added 140 commits

• 137ba4ee...a68440c4 - 139 commits from branch STJr:next
• e4db6cbc - Merge branch SRB2:next into ringflag

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added Unmergeable label

added 802 commits

• e4db6cbc...6d645acb - 801 commits from branch STJr:next
• c18ed685 - Merge branch 'next' into ringflag

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removed Unmergeable label

added 802 commits

• e4db6cbc...6d645acb - 801 commits from branch STJr:next
• c18ed685 - Merge branch 'next' into ringflag

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