Make several Lua global variables writable.

See merge request !1233

Improved sprite sorting against 3d floors

See merge request STJr/SRB2!1235

Can't use gz/gzt because there is no transformation to make those work
differently for splats.

Flame Shield & Thunder Shield Adjustment (Closes #363)

Closes #363

See merge request STJr/SRB2!1220

Made height/spinheight and height change values in replays more accurate

See merge request STJr/SRB2!1241

Make the replay camera follow the player

See merge request !1243

Remove unused music type enums

See merge request STJr/SRB2!1253

Uncap palette lump palettes & allow flashpal palettes to display during pause

See merge request STJr/SRB2!1255

Echo filenames when compiling without ECHO=1

See merge request STJr/SRB2!1260

New sprite features

See merge request STJr/SRB2!1257

Update R_DrawFloorSprite_NPO2_8 and R_DrawTranslucentFloorSprite_NPO2_8 to have the lastest NPO2 optimizations

Use SDL version of executable icon at runtime on macOS

See merge request STJr/SRB2!1250

UDMF: Multitag support

See merge request !1097

Expose more music functions to Lua

See merge request STJr/SRB2!1230

Don't let Lua set cvars that have CV_NOLUA

See merge request STJr/SRB2!1245

Fix potential crash with precipitation in OpenGL

See merge request !1249

Reallow P_MobjSpawn to change the scale of objects spawned from mapthings

Closes #328

See merge request !1251

Remove direct definition for D__USE_MINGW_ANSI_STDIO, as the latest standards consider this to be deprecated.