Replaces Flicky List system from 2.2.
Specify a list of comma-seperated Followers.
Not used by any systems in this commit, but important to store the data for later.
All typedefs for structs that were present in other header
files have been moved to here. (Except node_t because the
renderer and netcode both define node_t LOL.)
- Refactor significantly (now has its own func, `G_GetNextMap`)
- If gametype uses cups, iterate through cups to find the current level, then grab the next valid level
- If not, get the next valid mapheader for your gametype
- SOC `nextmap`/`marathonnext` is not just deprecated but REMOVED
- Hide the NEXTMAP_ constants again, but leave support dummied out for if we have them publically accessible again
- Also get rid of a bunch of OTHER mapheader stuff we're never gonna use
- NiGHTS Grades? NOPE
- Vanilla titlecard patches? NOPE
- Boss music fadeout/replacement? NOPE
- Select Heading? NOPE
- You've been blocked.
- Don't show maps without lumps on the level select list
- this is me being petty, but making it NOTIMEATTACK in SOC instead of TIMEATTACK so we can reconsider the maps with/without them.
