Hack P_SpawnHoopsAndRings into little pieces

See merge request !572

More customisable title card

See merge request !552

Wipe styles cleanup

See merge request !525

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

See merge request !551

OpenGL GIF movie recording

See merge request !549

Fix model texture blending

See merge request !546

Init MUSICDEFs regardless of music state

See merge request !532

Fixed missing break in offset handling for horizontal springs

See merge request !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 !530

Hack P_SpawnMapThing into tiny little pieces

See merge request !564

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