* Change sanitization check for `ExportDataAsCode`

I opted to use `isalnum` function since it should handle most cases. It
cannot however handle cases of files beginning with numbers.

* Update `ExportDataAsCode` condition

* Reinsert comment on `ExportDataAsCode`

* Fixed some grammar mistakes.

* Fixed some typos.

This immediately shows log messages when stdout is not connected to a
tty.

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.

rlgl has been redesigned to avoid any dependency to `raylib` or `raymath`, all functions using some of those libs have been reviewed.
 - REMOVED: `Texture2D`, `Shader` structs dependency
 - REMOVED: `Vector3`, `Matrix` structs dependency
 - REMOVED: raymath functions dependency, all required math is implemented in rlgl
 - ADDED: `rlMatrix` custom rlgl type
 - ADDED: `utils.c`: `rlMatrixFromMatrix()` and `rlMatrixToMatrix()` for a safe conversion between raylib<->rlgl matrix types
 - ADDED: `rl` prefix to all `rlgl` structs
 - Other small tweaks here and there

* Unused UWP define removal

* Further removal of unusued UWP defines

Removed memory allocation callbacks

This new flag allows omitting stdio.h library in case of a custom implementation is used.

NOTE: This feature is still under consideration and not complete.

I feel nobody has ever used this function...

Exposing internal memory allocator/free, useful for advance users when required