Support custom memory allocators

[raysan5]

raylib implements RL_MALLOC, RL_CALLOC, RL_REALLOC and RL_FREE but some of the external libraries implement their own memory allocators definitions, others none at all.

Below table shows allocators used by external libraries used by raylib, all of them should be custom allocators to have full control over raylib programs memory allocation if it was required, for example on embedded devices.

library	custom alloc	custom free	others	state
glfw	calloc()	free()	realloc()	❗️
glad	-	GLAD_FREE	GLAD_REALLOC	✔️
miniaudio	MA_MALLOC	MA_FREE	MA_REALLOC	✔️
stb_image	STBI_MALLOC	STBI_FREE	STBI_REALLOC, STBI_REALLOC_SIZED	✔️
stb_image_write	STBIW_MALLOC	STBIW_FREE	STBIW_REALLOC, STBIW_REALLOC_SIZED	✔️
stb_image_resize	STBIR_MALLOC	STBIR_FREE		✔️
stb_vorbis	malloc()	free()		❗️
dr_flac	DRFLAC_MALLOC	DRFLAC_FREE	DRFLAC_REALLOC	✔️
dr_mp3	DRMP3_MALLOC	DRMP3_FREE	DRMP3_REALLOC	✔️
dr_wav	DRWAV_MALLOC	DRWAV_FREE	DRWAV_REALLOC	✔️
jar_mod	JARMOD_MALLOC	JARMOD_FREE		✔️
jar_xm	JARXM_MALLOC	JARXM_FREE		✔️
par_shapes	PAR_MALLOC	PAR_FREE	PAR_CALLOC	✔️
cgltf	CGLTF_MALLOC	CGLTF_FREE		✔️
dirent	DIRENT_MALLOC	DIRENT_FREE		✔️
rgif	RGIF_MALLOC	RGIF_FREE		✔️
tinyobj_loader_c	TINYOBJ_MALLOC	TINYOBJ_FREE	TINYOBJ_REALLOC, TINYOBJ_CALLOC	✔️

NOTE: stb_vorbis and glfw implement custom allocators mechanism based on functions pointers... but it will be nice to be able to also re-define default allocators.

Below table shows allocators used by raylib modules.

raylib module	custom alloc	custom free	others	state
core	RL_MALLOC	RL_FREE		✔️
rlgl	RL_MALLOC	RL_FREE	RL_CALLOC, RL_REALLOC	✔️
text	RL_MALLOC	RL_FREE	RL_CALLOC, RL_REALLOC	✔️
textures	RL_MALLOC	RL_FREE	RL_REALLOC	✔️
physac	PHYSAC_MALLOC	PHYSAC_FREE		✔️
rnet	RNET_MALLOC	RNET_FREE	RNET_CALLOC	✔️
rmem	malloc()	free()		✔️

Note that all libraries custom allocators should ultimatelly fallback to raylib allocators: RL_MALLOC, RL_CALLOC, RL_REALLOC, RL_FREE.

[raysan5]

Reviewed some raylib allocations in commit bec4677.

[raysan5]

jar_mod and jar_xm reviewed in commit d797bb3

[raysan5]

rnet allocators reviewed in commit 1c4dadc. Just note this file should actually be redesigned...

[raysan5]

dirent.h module reviewed in commit edc1d25.

[raysan5]

glad.h module reviewd in commit cff3830. Note that this module load a bunch of extensions that are actually not required; raylib only uses a minimal subset of OpenGL. Maybe extensions loading could be restricted to used ones only...

[raysan5]

cgltf.h updated in commit e932d23.

[raysan5]

This issue is related to #966. Supposedly, new raylib module rmem can be used to manage ALL memory required by raylib and it's dependencies.

[raysan5]

stb_vorbis implement custom memory allocation mechanisms based on malloc()/alloc()/free().

glfw just removed cutom allocators option and relies primary on calloc()/free().

I can not do much on my side about it at the moment... so, closing this issue.