REDESIGNED: `LoadDirectoryFiles()`
ADDED: `LoadDirectoryFilesEx()`
REDESIGNED: `LoadDroppedFiles()`
ADDED: `IsPathFile()`

This BIG BREAKING change simplifies the functions and gives more control to the user:
 - A new `struct FilePathList` has been added to avoid exposing complex pointers.
 - User is responsible of memory loading/unloading
 - Filepaths loading support recursive directories and file extension filters

RENAMED: `ClearDroppedFiles()` to `UnloadDroppedFiles()`

Now rlgl uses the `Matrix` type, just make sure it has been previously defined somewhere... I don't like this approach but it's probably the easier one for the users... still looking for a better solution... maybe using something like
`#define MATRIX_TYPE`, so it can be checked in other modules.

* Fix some warnings in examples.

* cleanups from review

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

Some enums values have been renamed to be more consistent and also provide a more detailed description:
 - ShaderLocationIndex:    LOC_VERTEX_POSITION -> SHADER_SHADER_LOC_VERTEX_POSITION
 - ShaderUniformDataType:  UNIFORM_VEC2 -> SHADER_UNIFORM_VEC2
 - MaterialMapType: MAP_ALBEDO -> MATERIAL_MAP_ALBEDO
 - PixelFormat: UNCOMPRESSED_GRAYSCALE -> PIXELFORMAT_UNCOMPRESSED_GRAYSCALE

Updates skybox demo to show how to do both HDR and non HDR skyboxes

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

Added some tracelog messages

Now supports dynamic panoramic view, just drag and drop

* Fix bug #1270

Added an argument to the shader in order to flip the texture

* Fix Bug #1270

* Fix bug #1270

They are not automatically unloaded when unloading the model!

When using FormatText() several times in same function, returned string is static and so, the same is returned, resulting in failures on shader loading.

Note that HDR exposured possibilities are not used on this example...

- Renamed Begin3dMode() --> BeginMode3D()
- Renamed Begin2dMode() --> BeginMode2D()
- Renamed End3dMode() --> EndMode3D()
- Renamed End2dMode() --> EndMode2D()

RAYMATH_EXTERN_INLINE was renamed to RAYMATH_HEADER_ONLY, which user code
may define if they want to use it as header-only library. If multiple
files in the same project define RAYMATH_HEADER_ONLY, they might each
have duplicate out-of-line definitions of the same functions.

By default, raymath.h exposes inline definitions, which instructs the
compiler _not_ to generate out-of-line definitons, if out-of-line
definitions are required, those of the file defined with
RAYLIB_IMPLEMENTATION are used instead. There may be only one such file.

In C++ mode, the compiler will select only one out-of-line definition
automatically, so no need to define a RAYLIB_IMPLEMENTATION.

Unfortunately, we have to remove raymath function declaration from
raylib.h as those declarations would lead to duplicate out-of-line
definitions which would yield linker errors. This problem didn't
exist with GNU89 or C++, because there multiple defintions are ok,
but in C99 they aren't.

This reverts commit 6ffc8cb799.
and commit e4d7bbec1e.
which I pushed by mistake...

RAYMATH_EXTERN_INLINE was renamed to RAYMATH_HEADER_ONLY, which user code
may define if they want to use it as header-only library. If multiple
files in the same project define RAYMATH_HEADER_ONLY, they might each
have duplicate out-of-line definitions of the same functions.

By default, raymath.h exposes inline definitions, which instructs the
compiler _not_ to generate out-of-line definitons, if out-of-line
definitions are required, those of the file defined with
RAYLIB_IMPLEMENTATION are used instead. There may be only one such file.

In C++ mode, the compiler will select only one out-of-line definition
automatically, so no need to define a RAYLIB_IMPLEMENTATION.

Unfortunately, we have to remove raymath function declaration from
raylib.h as those declarations would lead to duplicate out-of-line
definitions which would yield linker errors. This problem didn't
exist with GNU89 or C++, because there multiple defintions are ok,
but in C99 they aren't.

Reorganizing folders
Review examples
Work on makefile and loader.html

raylib webpage has been completely reorganized and moved from gh-pages
(a pain to work with) to docs folder. Useless libs have been removed,
webs have been renamed, etc.

Now it would be easier (hopefully) to update webpage. :)