npe: add popen and pclose

inttypes.h: add more PRI*; remove "d" suffix because *printf are the ones exported

sdl2: SDL_WaitEvent(NULL), SDL_PushEvent (thanks cgnarne)

sdl2: mixer: fix a warning

sdl2: assortment of fixes and funcs (thanks moody)

sdl2: add SDL_MIX_MAXVOLUME (thanks moody)

errno: add EACCES (thanks moody)

npe: add atime to *stat

npe: add clock_gettime

sdl/audio: set pipe buffer size when running pcmconv; use the correct device name

sdl2: refactor image channel code, more palette function coverage

SDL: readjust/add more scancodes

SDL: scancodes: place command & period properly (thanks uramekus)

sdl2: add SDL_PIXELFORMAT_ABGR8888

sdl2: add SDL_LockTexture and SDL_UnlockTexture

parg: fix a few warnings

npe: add getopt and getopt_long (based on parg)

npe: add strerror_r

pthread: fix const/pointer mess

npe: add cbrtf