Reduce size of SPLASH lump

Minor tweaks

Minor tweaks to some messages

Alert monsters if attacked during 2nd frame of idle animation

See information about this by axdoomer here: https://www.doomworld.com/forum/post/2125618

No screenshots when not playing game if +screenshot not bound to PRTSCR

Minor tweaks

Fix potential heap corruption upon loading savegame

Thanks to Lila Feuer and danieldx on the Doomworld forums!

Tweaks to some things' alternate names

Fix segmentation fault when running on rgb565 screen

Taken from Chocolate/Crispy/Woof

Exit with error if texture missing patch

Because its only going to cause a crash later.