Created raylib libc dependency (markdown)

raylib-libc-dependency.md

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+raylib is a C library and inevitably it depends on some implementation of [C standard library (libc)](https://en.wikipedia.org/wiki/C_standard_library). 
+
+While working on raylib 3.0 I took some time to analyze that dependency in detail, no plans to remove it (maybe minimize it a bit) but I think it could be useful to have the knowledge where it is required.
+
+### stdlib.h
+
+| module | libc function   | raylib function   |
+| :----: | --------------- | ----------------- |
+| core                   | srand()         | InitTimer()      |
+| core                   | abs(), rand()   | GetRandomValue() |
+| core                   | atexit()        | InitKeyboard()<br>InitTerminal() |
+| shapes                 | fabs()          | CheckCollisionCircleRec()<br>GetCollisionRec() |
+| utils                  | exit()          | TraceLog()       |
+
+### stdio.h
+
+Note that file loading functionality is currently being centralized to `LoadFileData()`/`SaveFileData()`, most of the file access calls below will disappear soon, replaced by memory buffers parsing.
+
+| module | libc function   | raylib function   |
+| :----: | --------------- | ----------------- |
+| text                   | fopen(), fseek(), fread(), fwrite(), fclose()    | LoadBMFont()  |
+| text                   | fgets()                | LoadBMFont()   |
+| textures               | fopen(), fseek(), fread(), fwrite(), fclose() | ExportImageAsCode()<br>LoadDDS()<br>LoadPKM()<br>LoadKTX()<br>SaveKTX()<br>LoadPVR()<br>LoadASTC() |
+| models                 | fopen(), fseek(), fread(), fwrite(), fclose()  | LoadIQM()<br>ExportMesh()<br>LoadModelAnimations()  |
+| audio                  | fopen(), fseek(), fread(), fwrite(), fclose()  | ExportWaveAsCode()<br>LoadWAV()<br>SaveWAV()                                                       |
+| utils                  | sprintf()  | TraceLog()    |
+| utils                  | fopen(), fseek(), fread(), fwrite(), fclose() | LoadFileData()<br>SaveFileData() |
+
+### string.h
+
+| module | libc function   | raylib function   |
+| :----: | --------------- | ----------------- |
+| core                   | strlen()   | GetFileNameWithoutExt()<br>GetDirectoryPath()<br>GetPrevDirectoryPath()<br>OpenURL()<br>InitEvdevInput()     |
+| core                   | strrchr()  | GetExtension()<br>EventThreadSpawn()  |
+| core                   | strcmp()   | IsGamepadName()<br>EmscriptenKeyboardCallback()  |
+| text                   | strcmp()   | TextIsEqual()   |
+| text                   | strcpy()   | TextAppend()<br>TextReplace()   |
+| text                   | strncpy()  | TextToUtf8()<br>TextReplace()   |
+| text                   | strcat()   | TextJoin()         |
+| text                   | strstr()   | *several funcs.*     |
+| textures               | strlen()   | ImageTextEx()      |
+| raudio                 | strcmp()   | IsFileExtension()  |
+
+### math.h
+
+| module | libc function   | raylib function   |
+| :----: | --------------- | ----------------- |
+| models, shapes, camera | sinf(), asinf(), cosf()<br>acosf(), sqrtf(), atan2f()              | *several funcs.*     |
+| raymath                | sinf(), cosf(), acosf(), tan()<br>fabs(), sqrtf(), fminf(), fmaxf() | *several funcs.*     |
+| core                   | tan()                                                            | BeginMode3D()        |
+| rlgl                   | atan2()                                                          | SetVrConfiguration() |
+| text                   | sqrtf()                                                          | GenImageFontAtlas()  |
+
+### stdarg.h
+
+| module | libc function   | raylib function   |
+| :----: | --------------- | ----------------- |
+| text   | va\_list, va\_start(), vsprintf(), va\_end()   | TextFormat() |
+| utils  | va\_list, va\_start(), vsprintf(), va\_end()   | TraceLog()   |