Hack P_SpawnHoopsAndRings into little pieces

See merge request STJr/SRB2!572

More customisable title card

See merge request STJr/SRB2!552

Wipe styles cleanup

See merge request STJr/SRB2!525

The "SRB2" directive, for warning if a SOC isn't compatible

See merge request STJr/SRB2!551

OpenGL GIF movie recording

See merge request STJr/SRB2!549

Fix model texture blending

See merge request STJr/SRB2!546

Init MUSICDEFs regardless of music state

See merge request STJr/SRB2!532

Fixed missing break in offset handling for horizontal springs

See merge request STJr/SRB2!571

-Hoops are spawned in P_SpawnHoop
-Item patterns are spawned in P_SpawnItemPattern
-Ring-like items are spawned normally via P_SpawnMapThing
-Bonus time items are spawned via P_SpawnBonusTimeItem, which is a wrapper for P_SpawnMapThing

Handle signals correctly on linux

See merge request STJr/SRB2!530

Hack P_SpawnMapThing into tiny little pieces

See merge request STJr/SRB2!564

Replaced functions for spawning premade rows of rings with a function for spawning a generic row of rings (groundwork for UDMF)