Add Precache + Add functions to play sounds
Entity header + API functions + Fixes

Add entity header.
Add macros for bitwise operations.
Add new API functions.
Fix the function Kr_Sound_Play.
Add a check in UTIL_PlaySound.
Engine wrappers + Entity data + A lot of fixes...

Add engine wrapper functions.
Change *_Free to *_Quit for some functions.
Add entity data.
Change "screen" to "renderer".
Do a lot of fixes...