Feel free to reorganize as necessary.

Zoning out

See merge request STJr/SRB2Internal!133

# Conflicts:
#	src/sdl/i_system.c

Linux limbo

See merge request !228

SOC sanitizing

See merge request !227

Console key breakfast

See merge request !226

Turns out compiling for Linux 32-bit using the Makefiles never actually defines LINUX! Apart from that, most of the existing Linux-specific code in SRB2's source code (except for tmap.s) actually uses __linux__ instead anyway

Eat unprintable keys too, since there's no reason to feed them to G_Responder anyway when the console is open

Make CON_Responder eat Ctrl+key combos that have no effect, instead of passing the key on to G_Responder

Total reorganisation of z_zone.c/h, added doxygen-compatible comments to all functions and additional regular comments where appropriate, changed purge tag macros to an enum list

Clean up z_zone.h's function protos to look more readable like m_random.h, don't name functions with "2" if not using PARANOIA or ZDEBUG

also, Z_Malloc/Calloc/Realloc are now macros of the "Align" versions, regardless of ZDEBUG or not

Fix net commands not always being freed

File loading cleanup

See merge request STJr/SRB2Internal!129

Fix SOC/Lua loading messages to display full names or even display at all (for PK3s at least), and otherwise some cleanup of existing code for the messages.

Also, I moved lua_lumploading on/offing to LUA_LoadFile.

Stop leaking names via metadata.

See merge request !223

Fix for "playdemo" not working with custom home paths

See merge request !221

Hotfix for "LUA PANIC" crash when joining a netgame

See merge request !222

General sky fixes

See merge request STJr/SRB2Internal!132

Fixed sky-sky thok barriers showing HOM (turns out the floor and ceiling share the same plane, so I've modified the code to account for this)

Additionally, place some optimisations in both software and OpenGL; in particular one has been added for when all of back and front sector (floor and ceiling) is sky: since everything is "open" anyway, we can simply the usual checks involved.

Thankfully it was really just a copy+paste of the code I already tinkered with for the normal ceiling sky based thok barriers, but tweaked for floors instead

Cleanup of the code I've tweaked for skies, added SLOPEPARAMS macro to R_StoreWallRange for use in getting seg end z positions

cv_playername already has a valid default value of "Sonic". We do NOT need to expose things like this.

some cleanup of software's seg rendering code, moved Red's polyobject plane hack to R_StoreWallRange since it doesn't actually need to be done every column draw

(I suspect polyobject planes don't actually need the minx/maxx hacks anymore, but I haven't the time to test that tonight nor is this branch really suited for it anyway)